Architect masterplans £200m development that could include a 43-storey tower next to London landmark.
Architect Allies and Morrison is planning a £200m development including a tower that could go next to Foster and Partners' Swiss Re building in the City of London.
The architect has worked with consultant Gardiner & Theobald to draw up plans for a 43-storey tower on a site that includes 61 St Mary Axe. Foster's 41-storey tower is located at 30 St Mary Axe.
The developer, Great Portland Estates, has combined a number of its land holdings in the City to produce a two-acre site on which it aims to create an office and retail development.
As well as 61 St Mary Axe, Great Portland also has holdings on nearby sites at Bishopsgate and Camomile Street.
Robert Noel, property director for Great Portland Estates, said the firm had yet to decide on the form that the development would take.
He said: "We are in the early stages of masterplanning. At the moment it is unclear how tall or short or wide we'll go. We're considering options, one of which is a tall building."
Noel added that the decision on whether to develop a tall building would depend on commercial considerations.
Sources close to the scheme believe that the site can easily accommodate a tall building.
The site is ringed by several large schemes planned for the City that are currently on hold. However, one source close to the scheme said he remained confident that the project would move forward despite the slow progress of comparable city tower designs such as the Minerva Tower and the Heron Tower.
He said: "It's an issue of commercial sense and where the demand for this is coming from. But if I were a betting man, I'd say it was very likely to happen."
Great Portland Estates is understood to be deciding on its options in the next couple of months. It intends to submit a planning application in late summer.