Developer Helical Bar has given contractor John Sisk the go-ahead to start work before Xmas on the extensive remodelling of a major office block at Old Street in London.

The firm will strip the existing offices back to the frame and then extend the building out and upwards before recladding at a cost of £70m.

The Tower at 207 Old Street, which was previously home to Amec,  is the second phase of The Bower development next to Silicon Roudabout where properties prices are soaring in the face of demand from tech companies for space..

This phase will provide 170,000 sq ft of office space and 7,300 sq ft of retail/restaurant space, on completion of the works.

Existing block and remodelled building

207 Old Street was constructed in the 1960s and overclad in the 1980s. The existing block will now be stripped back to the concrete frame and raised by two floors.

Its 60s slab architecture will be broken up with a full height steelwork extension to the front of the building. On the ground floor, a generously-sized portion of the building will be cut out to create a pedestrian link from Old Street through to Baldwin Street.