A property developer whose extension blocks light to Sir David Hare’s writing studio in Hampstead has said it is impossible to criticise the work before it has been finished – despite it being deemed illegal.

Bahrain-based property developer Al Eshaq said he is stuck in limbo after Camden Council ordered him to pull down the illegal two-storey extension in Old Brewery Mews in November 2010.

He is reluctant to demolish it and instead wants to make improvements.

The illegal building work overlooks Bafta-winning playwright Sir David’s Grade II-listed studio, which he has owned for 20 years.

Mr Eshaq, who bought his property more than 30 years ago, says he received poor advice from planners who told him the work did not require permission.

He has now submitted an application to improve it and says the latest plans to modify what neighbours have branded a “hideous eyesore” will transform the shell.

In a letter to the Ham&High, Mr Eshaq said: “How [can] any responsible person or body can make any judgement on this extension when it has no windows installed and only has timber boarding?”

Neighbours have called for the council to pull down the two-storey extension.

Planning boss Cllr Valerie Leach said prosecution proceedings are underway.

A public consultation on the replacement extension runs until next Thursday.