Consultant Turner & Townsend has landed one of the most important contracts in its history – a £20 000 job with anxious clients, an inflexible deadline and a difficult brownfield site.

The job is to project-manage a nursery for No 10 Downing Street, ready for the arrival of the Blair baby at the end of May. Details of the project are sketchy, but it may involve putting up some shelves. Sources were tightlipped about whether the fit-out specification would involve pink or blue teddy bear wallpaper.

Sources said the firm would also oversee repairs to other rooms at No 10 and No 11. “It’s being driven partly by the nursery and partly by changes at No 10 and No 11,” said one.

It is understood that two contractors are competing for work.

After hearing that Cherie Blair was expecting, chancellor Gordon Brown said in January that he would move out of his flat at No 10 to give the family more space. The Blairs already have a four-bedroom flat above No 11 and No 12.

A No 10 spokeswoman refused to comment on the scheme. She said: “We do not brief on the private plans of the prime minister.” Turner & Townsend also refused to comment.

Cherie Blair made it clear recently that she expected her husband to take paternity leave after the baby was born, but the prime minister said he had not yet made up his mind.