The Dorset steelwork specialist has issued a claim against Gear for £723,000 plus legal costs on the Riverbank Plaza Hotel project on the Albert Embankment.
At least one other subcontractor on the job, M&E firm RTT, has since gone bust, while Danish bathroom pod manufacturer Barde Cabiner is also understood to be in dispute with Gear over non-payment on the project.
Another subbie on the hotel scheme was Northampton metalwork specialist Discain. Director David White said: 'We took them to adjudication and won £13,000. All I will say is that they promise you the sun, moon and the stars.'
Gear invited Bourne Steel onto the job under a £4 million contract in 2002 after the demise of original steelwork contractor Wescol. It began work on site in spring 2003 with works completed in March 2004 but the project was dogged by delays and payment problems.
Managing director David Sands said: 'We have been trading for 60 years and have never had to take such action. We have tried every route to get the money.
'We were in negotiations between October 2004 and May 2005, and went to mediation in September 2005, but Gear terminated process before it had been exhausted.'
He added: 'The hotel design was substantially changed and when that happens you get delays and payment issues. All in all it ended up with us doing in excess of £6 million - the money we're claiming is the final payment.
'We are fortunate. We are trading strongly and we have been able to make provision for the money outstanding. But there are others who were not able to take the strain as we and there were a number of subbies on the job who went bust, either on the job or soon after.'
Gear is preparing an acknowledgement to Bourne's claim, which was issued on May 30.
Chris Hough, Gear's legal representative, said: 'My client will be defending the claim vigorously and will be pursuing a substantial claim for damages for delay and other matters against Bourne Steel.'