Workmen unhappy about an unpaid bill sneaked into a university building to steal back the windows they had installed.

Staff happily waved them into the University Centre Hastings and even cleared students out of a classroom so the men could remove the glass panes.

They walked out with six windows, each bigger than a metre square, and loaded them into a van.

To get into the centre, staff from Portsmouth-based Pro-Fix pretended they had come to fix a leak.

They then took out the windows in protest that their £40,000 invoice is still outstanding.

The firm, which put in 44 windows in two stages in October 2004 and February this year, is in dispute with the main building contractor.

Rok, based in Eastbourne, said it had not paid up because there was a conflict about the subcontractor's performance.

Pro-Fix said it had done nothing wrong and took the windows as a last resort because attempts to discuss the matter had been unsuccessful.

Commercial manager Paul Osborn said: "Rok have refused to pay. We have written to them, we have spoken to them, we have tried everything.

"We are only a £2 million company. Forty thousand pounds for nine months is hurting us badly."

The windows were taken out on Wednesday.

Mr Osborn said: "It was a token gesture. I can't believe we got as far as we did.

"We just turned up and signed in the security book as normal and went in. They even got a roomful of students to move for us. We removed the glass without causing any damage."

Tariq Khwaja, marketing manager for the centre's site-management company SeaSpace, said: "Between 11am and midday the contractor entered the building and said they had come to fix a leak.

"Apparently they carried the windows out and loaded them into a van. Staff at the university were expecting someone to come and fix the leak. We did have staff who tried to stop them.

"It is an unusual tactic. We were taken by surprise."

Afterwards three windows were fixed with spare panes and three were boarded up.

Rok said there was a dispute over the amount owed because of "delays, defects and other attendance issues".

Area director Mike O'Callaghan said: "As a local business we pride ourselves in our relationships with customers, subcontractors and suppliers so we are naturally disappointed that Pro-Fix has decided to take the action it has.

"We refute the allegations that we have not been in communication over their account.

"They are aware there are unresolved issues in relation to their performance and there is a mechanism built into the contract for resolving such issues.

"Regrettably Pro-Fix have decided to act outside the contract.

"Their actions have been reported to the police and an injunction will be sought against them.

"In the meantime, efforts to resolve the dispute are progressing. Rok and the University Centre Hastings are in close contact to prevent any disruption to users of the building."