Foster and Partners’ iconic Swiss Re tower has scooped this year’s RIBA Stirling prize, the most prestigious award in British architecture.

The decision to bestow the top award to 30 St Mary Axe, to give the tower its official name, was made unanimously for the first time in the award’s history.

The judges, who included Angel of the North designer Antony Gormley, said that the Erotic Gherkin – to give it its unofficial name – was already a popular icon on the London skyline.

They said: “The entrance is suitably elegant and impressive in scale. Similarly, the bar area at the top promises to respond to the challenge and opportunity of elevation, situation and view: it will be one of the very best rooms in 21st century London.”

George Ferguson, the RIBA president, presented Lord Foster of Foster and Partners with a cheque for £20,000.

The other shortlisted buildings were: the Kunsthaus in Graz, Austria, by Peter Cook and Colin Fournier; The Spire in Dublin, by Ian Ritchie Architects; the Imperial War Museum North in Manchester, by Studio Daniel Libeskind; the Phoenix Initiative in Coventry, by MacCormac Jamieson Prichard; and the Business Academy Bexley in Kent, also by Foster and Partners.