The gallery is now due to open in early 2007

The Middlesbrough Institute of Modern Art (Mima) was proposed following the success of Gateshead's Baltic complex.

Construction started in July 2004, with a grand opening due to take place before the end of this year.

But Mima director Godfrey Worsdale said environmental and security issues had yet to be resolved to enable the complex to house expensive artworks.

It is not now expected to open until 2007.

Mr Worsdale said: "The gallery is nearing completion and we had hoped that the tests on temperature and humidity would be complete by the end of the year.

'First class security'

"They won't be and that means it will be early in the New Year when we open our doors.

"I have charged our engineers with guaranteeing me very tight levels of humidity, temperature and light and rigorous first class security.

"When all those things are in place then I can go to the British Museum, the Tate gallery and museums abroad and tell them we are ready to have their Picassos, Warhols and Pollocks."

David Budd, Middlesbrough Council's executive member for regeneration, added: "Our partners who are funding Mima have been very understanding about what in the scheme of things, is a fairly short delay.

"I am sure that the thousands of local people who are looking forward to the opening will understand too that everything has to be absolutely right for such an important event for the town."