A five-storey Norwich office block could be partly converted into luxury penthouses and flats.

St Crispin's, in Duke Street, is on the market for £4.75m, with around 14 tenant businesses offering the new buyer a £785,000 income in rent.

But agents Arnolds Keys believe there is an opportunity to convert some of the building into flats with panoramic city views, with businesses continuing alongside them until their leases run out or are renewed.

The government has relaxed planning rules in this area, with permitted development rights allowing a change of use from offices to residential introduced for a period of three years from May 30, 2013 to May 30, 2016.

And this could change the face of Norwich, giving new life to unused office space.

Craig Knights, head of commercial and a partner at Arnolds Keys, said: 'The permitted development rights policy was borne out of a lack of residential properties and an oversupply of poor quality city centre offices so it solves two problems in one hit.

'In Norwich alone we are currently seeing just over 200,000 sqft of office space, tired offices which were not economically viable for refurbishment, being turned into 247 residential units so it is literally changing the shape of the city.

'The policy is working very well for Norwich which had a lot of poor quality office space which was in a downward spiral.'

St Crispins includes an enclosed atrium on a 1.71 acre site with parking for 33 vehicles and it has its own cafe area and a total of 115,050 sqft of space.

St Crispins was opened in 1976 to provide extra space for Her Majesty's Stationery Office staff. It is now occupied by The Stationery Office; Banner Business Services, Countrywide Ltd and Central Mortgages among others.