An investigation is set to be launched into claims by Conservatives in Bradford that a ballot box containing postal votes was deliberately tampered with.

Senior regional Tories are due to meet council officials this week to discuss the claims.

The furore arose at the Richard Dunn Sports Centre on local election night on Thursday as the box containing votes for the Little Horton ward was about to be opened. Jamshed Khan, agent for the Tory candidate Khadam Hussain, asked for the seals to be checked and it emerged that one of them had been broken.

The Tories claim the ballot box was deliberately tampered with and vote papers altered. They also say one of the seal numbers was different to what they had been given before the election.

Mr Khan called in police, who were present at the poll, to witness the broken seal and there were heated scenes between Tories and Labour officials.

The controversy delayed the count, which ended with Labour leader Ian Greenwood retaining his seat, beating Mr Hussain by a slender 178 votes.

Mr Khan said he was now waiting to hear from the regional Conservative office as to what action it planned to take.

Mr Hussain, a 52-year-old businessman, rejected explanations that the seal was broken in transit from the town hall to the sports centre. "The papers were in the box in bundles of 50 with rubber bands round them," he said. "But when the box was opened they were all loose.

"I am absolutely sure they were deliberately tampered with. These are very strong seals - I don't believe they could have been damaged in transit."

Mr Hussain said the box should have been "put in quarantine" and forensically examined before "This might happen in the Third World, but it shouldn't happen here in the 21st century," he said. "I hope to overturn the result."

John Hardy, secretary for the Bradford and Shipley Conser-vative Federation, said the matter had been discussed between council leader Margaret Eaton and chief executive Ian Stewart.

He said there would then be a meeting next week between him, a representative from Conser-vative central office, Councillor Eaton, and a representative of the chief executive.

He said: "We are not taking it lightly. We want to know the truth. It is the second successive year the Little Horton box has been subject to potential problems. It's interesting it's happened twice in that one ward when there are 30 wards."

Council chief executive Ian Stewart said so far no complaint had been received.

"There were two seals," he said. "One was broken in transit. Staff resealed the ballot box, witnessed by others."