»A developer who wants to build a 2,000-capacity conference centre in Finsbury Square has threatened to sue Islington Council in a row over the value of the site.

Will Bailey, founding director of Planit Events, said the council was fully behind the project in 2005-6 but went cold on the idea after a valuation of the land concluded it did not represent “best value” for the local authority, who are the leaseholders.

Mr Bailey said more than £1million had already been spent on the project. He said he had asked the local authority to see the original documents and emails relating to the valuation but they had so far refused his requests.

The council said that planning permission was granted in 2005 but it was not implemented. A second application was submitted in 2006 but was not given consent because of legal agreements not signed by the developer.

Mr Bailey said: “If I find out the council has fabricated the report we will have no option but to sue them.”

The underground conference centre would host charity dinners, awards ceremonies and exhibitions and be a “huge employment” opportunity for the area, claimed Mr Bailey. It would also offer 20 days of community use free of charge.

Two valuations carried out on behalf of Planit Events claimed the development would be worth £2million – £1million more than what it is worth now, he said. “We’re missing out on a huge employment opportunity.”

An NCP car park, a restaurant and bowling green currently occupy the square.

A council spokesman said: “Islington Council has an obligation to seek best consideration for land it holds. Separately, we have a role in determining planning applications and the applicant here was unable to complete the necessary legal agreement.”