ST JOHN'S is to build a new quadrangle behind St Giles in one of the biggest development schemes undertaken by an Oxford college for years.

The new quad will be similar in size to the college's historic Canterbury Quad, widely recognised as one of the most impressive in the city.

On St Giles itself, two new gardens are to be created bringing the famous sequence of gardens running through St John's beyond the college walls, to extend the "green lung" into the city centre.

And as well as increasing in-house accommodation for students, St John's also promised "to contribute to the cultural life of Oxford" by creating a performance space that will be made available to the public.

The multi-million pound development will be known as the Kendrew Quadrangle, after the former St John's President Sir John Kendrew, a Nobel Prize-winning molecular biologist.

The new quad will be built on the site of the former Queen Elizabeth House, once the home of the university's international development department, part of which will be demolished.

A spokesman for the college said: "The cost will be considerable. We see this as an essential investment that will secure the college's future as a leading academic community.

"In order to continue to attract the most able students and academics to St John's we need to offer top-class facilities. Currently we do not have enough accommodation to house all our postgraduate and academic members in college, an advantage we have for some years been able to offer to all undergraduates.

"To do this, we intend to create a new building on land just to the north of the college with an entrance on to St Giles, a little beyond St Giles House and pedestrian access from behind the Lamb and Flag.

"The main part of the building is set behind 20 to 23 St Giles, minimising the impact on the street itself. Our intention is to create a first-rate building in the modern idiom."

As well as creating a new landmark building north of the college, there are plans to restore the older listed buildings on the site, including a 17th-century barn, which would be converted into a new exhibition and performance space.

The idea of extending the college gardens into the "public realm" will be viewed as part of efforts to make St John's more accessible.

A glass slot over the main entrance will allow views from St Giles into the heart of the new quad.

The chairman of Oxford Civic Society, Tony Joyce, welcomed the scheme. He said: "This is one of the more significant major additions to one of the larger Oxford colleges for quite some time.

"I think it is an exciting development. St John's is obviously keen to produce a fine building worthy of the rest of the college's buildings. St John's own such a large part of the frontage of St Giles, that it is their responsibility to retain one of the most striking parts of the Oxford scene."

A planning application will be submitted later this month, with the college hoping building work can begin in the spring of 2008. Restoration work on 20 and 21 in St Giles and The Barn - pictured left - began last autumn.

The new building will house 65 students in study-bedrooms, and will also include café and basement areas, a gym and rooms for music practice. It will also offer library and archival facilities in the east wing and a number of teaching rooms in the west wing.

The Garden Quadrangle at St John's was voted the best building erected in Oxford in the last 75 years, in a poll organised by The Oxford Times five years ago.

Debbie Dance, director of the Oxford Preservation Trust, said: "The restoration of the buildings in St Giles should look splendid, while the glimpses of the new quad and a large old beech tree should add to the street scene."

St John's, Tony Blair's former college, says it is investigating a series of sustainable fuel options.