It's not easy being a building control officer – you have to be exacting yet diplomatic. We spent the day with three honchos from Southwark council and found out what eventful lives they lead – that, and not to go on a roof alone with an angry builder …
What does construction think of Building control officers? Are they the forgotten heroes of the industry, who ensure that the buildings contractors put up are safe, efficient and comfortable? Or are they interfering busybodies tying up everyone in a load of red tape – a needless expense that everyone would be happier without? To find out more, Building spent a day with Southwark council's building control department.

Southwark is the ideal borough to find out what the typical urban officer does with their time, as it has a little bit of everything. It takes in landmark commercial projects such as Foster and Partners' City Hall at its northern boundary, in the southern suburbs of Dulwich there are row upon row of large Victorian terraces, and in the middle are the rundown council estates, some of which are being totally regenerated.

Southwark building control operates out of a grey slab of a building called Chiltern House on the rundown Aylesbury Estate in Peckham. It is on the ground floor, has 25 staff and is where advice is dispensed and all aspects of Building Regulations are checked and chased up. And it is where we set off on our journey with building control officer Robert Heath, who has worked for the council for 30 years.

10.00am: My flat is falling down
We set off in Heath's car to a dangerous structure reported by a member of the public. It is a shop on Southampton Way in the heart of Peckham; a builder adding a rear extension has taken down the rear wall without adequately propping it. "The owner of the flat above called us when she saw the floors and walls beginning to crack. We got down there pretty quickly," says Heath. "This is what happens when inexperienced people start doing work. They had no idea."

After finding a parking space – "Parking is one of the worst things about this job; there are very few places without yellow lines" – Heath goes to talk to the Cypriot owner of the corner shop, who has employed a fellow countryman to do the work. We are greeted by a forest of emergency props supporting the remnants of the rear wall. Heath checks these, and tells the builder to fix a damaged drain immediately because of the food stored nearby. He writes this all down on a pad, gives it to the builder and keeps a copy for the council's records.

10.40am: The spot check
We set off to a nearby street to check a single-storey extension in Lyndhurst Road. On the way, Heath talks about people who start work without notifying building control. "A lot of it goes on," he says. "We get to know our patch. A lot of the homeowners don't realise they have to notify the local authority when they do building works. It's the smaller people." Heath is trying to find somewhere to park on Talfourd Road when he spots a house with a skip outside. "Look, there's one over there," he says.

Heath decides to make an unscheduled call.

He marches up to the house and knocks on the door. The builder who answers looks at us suspiciously, and tells us to wait. The foreman appears and invites us in. At the back of the house a conservatory is under construction. Heath asks why the floor screed is uninsulated. The builder says this is unnecessary because the doors between the house and the conservatory are staying – conservatories separated by a door from the main house are exempt from Building Regulations. Heath says he will check the plans back at the office, and if things are not as described a stiff letter will go out to the architect.

Outside, Heath says he cannot insist on an insulated screed as it would cost the client extra money – and they could claim the cost back if building control turned out to have insisted on it unnecessarily. We walk to the house Heath was originally planning to visit. The owner lets us in and shows us a single-storey extension at the back of the house. This is clearly a quality job: mahogany doors and very efficient double-glazed units. Heath checks the outside and, satisfied that the work conforms with the regulations, we leave.

11.30am: Beneath the floorboards
Ivydale Road, further south, is a long street of non-descript Victorian terraced housing. We enter another no-expense-spared refurbishment.

The ash stairs will contain glass panels and have a glass balustrade. Heath is more concerned about the structural integrity of the staircase which appears to be supported at the top by a single 6 × 2 in beam, which is embedded in a wall on one side. It is impossible to see how far the beam extends into the wall, so Heath asks for a floorboard in the neighbouring bedroom to be taken up for his next visit so he can check it. Outside, he says: "A lot of our job is helping the builder. They can be good, but still miss bits. We're like a second pair of eyes."

12.15pm: Under siege
The Hexagon Housing development in Medlar Street off Camberwell New Road is surrounded by razor wire. A wary site worker lets us through the gates, past a cage containing an Alsation and a Rottweiler, to the site hut. Adi Alsaeedy, Fairview Homes' site manager, says there is a siege in progress down the road – something to do with drugs and guns. He is also under siege: one of his neighbours is enraged because he is under the impression the council failed to carry out a proper consultation process. Alsaeedy is the third site agent on the job – two others left after being assaulted by the man.

Unfortunately, there is nothing the control officers can do about this, so they content themselves with checking the drains linking the yet-to-be built homes. A run linking two access chambers kinks instead of going in a straight line. Heath tells Alsaeedy that the drains have to be built as designed, adding that something like a nappy could block the drain where it kinks. "In the long term it could cause a problem, so they need to get rid of the problem now when there is an opportunity," he says.

12.55pm: The outpost
We travel back to Chiltern House to meet Bob Jones, who heads Southwark's building control department. He is going to show Building the other side of the control team's work, on the borough's commercial northern fringe. As we inch our way through congested streets, Jones explains why he has opened an outpost for three building control officers in Borough Market, by London Bridge. "It's very handy for people to come and see us," says Jones.

He says this is because of competition from control officers' bêtes noires: the private sector approved inspectors. Clients can elect to pay these inspectors to come and check their sites, rather than the local authority. Because of this, the council is trying to make life easier for its clients by locating an office near the big developments.

Free pre-application consultations are another technique to get clients to sign up to Southwark's services. Building control meets the architect and discusses a building's plans before they are submitted for formal approval. This gives the client a good idea of what is needed for compliance and should make the post-application inspection process much easier. Jones is on his way to meet architect Pringle Brandon to discuss the fit-out of plot 6 of the More London development near Tower Bridge. "Fit-outs are where the money can be made; the approved inspectors are aware of this, and this is where we are losing most of the work," says Jones. These council pre-applications cost the council up to 5% of the total value of the job, but "if we get the job it's half done already," says Jones.

1.15pm: The 'comfort letter'
At the meeting, Jones and his colleagues Andrew Bullivant and Ken Hughes go through the plans in detail with architects Nila Barnwell and Ashok Patel. They discuss issues such as finishes and the implications for fire regulations, signage for fire escape and the details of complying with disability regulations, including door widths and the location of handrails. At the end of the meeting, Hughes advises Barnwell to write the meeting up and send the notes in with the plans so he can issue a "comfort letter" – not a formal approval, but something to reassure the client that approval should be forthcoming.

3.00pm: The act of faith
After lunch, Hughes and Jones leave the office on foot for plot 6 as they are responsible for regulating the shell-and-core works. Hughes is checking the integrity of a drainage sump in the basement, and carries out a visual inspection. He says the only way to verify that it complies with the regulations is with a water test, but he isn't going to do one because it is a hard thing to do. Arup and concrete contractor O'Rourke would have tested it already, and Hughes has faith in the team: "The groundsman is a really solid bloke. I'd trust him with the Crown Jewels," he says. "We've got to draw the line somewhere so we can focus on the builders who don't have such high standards." Jones chimes in: "We spend proportionately more time on a single-storey rear extension than a big job like this, as the people who do that don't know what they are doing."

4.25pm: Leave it to the lawyer
Another short walk takes us to the trickiest problem of the day, off Bermondsey Street.

What we have is a residential development separated by a right of way from another residential development. The developer wants to put windows in the wall facing the neighbouring building, but the neighbour is concerned that if that happens, he won't be able to extend his property upwards.

The dilemma is that, if Jones allows the developer to put in his windows, and the neighbour's fears are realised, the council could be sued. On the other hand, the only sure-fire way to prevent this is to insist that the developer put in expensive recessed balconies – if the fenestration was set back from the boundary, the neighbour would retain the option to extend.

Jones offers his opinion: "In theory we could all sit around the table like a bunch of bureaucrats and say our developer can have the minimum amount of fenestration, meaning he would have to have recessed balconies. But we don't want to take that approach and would like to help this person – as it's very unlikely his neighbour would ever get planning permission." However, the final decision will be made by the council's lawyer.

5.30pm: Time to get some work done
Back at the office Hughes isn't clipping his briefcase shut ready for the journey home, but settling down for another two hours work. He says it's a good time to get some work done as he isn't interrupted by the telephone or constant meetings. This gives the lie to those who think government employees enjoy a cushy number– on the contrary, the team seemed highly dedicated, ready to help those who want advice, keeping faith in those who are clearly doing their job properly yet coming down hard on the cowboys. It's a potentially dangerous job, too. A few days later, speaking to Heath on his mobile, he was just going up on to a roof to check on a job that hadn't been notified. Heath was a little apprehensive – the roof is not a good place to be if the builders turn nasty …