A strong warning that people face prison sentences for the misuse of postal votes went out to candidates and election workers across the district today.

Candidates have also been warned in a letter from Bradford Council's Chief Executive Ian Stewart that results could be over-turned if their supporters are found to have abused the system.

He says it could also seriously damage the reputation of the party concerned and potentially have serious consequences for those involved.

Mr Stewart, who is acting returning officer for the district and in charge of elections for the five parliamentary constituencies, has sent out the letters following more than 17,000 applications for postal ballot papers.

Most applications came from the Bradford West and North constituencies where rumours have been rife about threats and intimidation over postal votes.

Police are investigating allegations that election workers are putting pressure on voters to hand over incomplete forms for the party activists to fill in.

Mr Stewart said today: "I have received allegations that postal voters are being encouraged to hand over incomplete postal votes. These are very serious accusations and I have warned candidates that results could be overturned if they are found to have won the election unfairly because their supporters have abused the system.

"Legal action could be taken and those concerned prosecuted if anyone is found trying to rig the system. I have passed details of the complaints to the police for investigation and arrangements have also been put in place to identify potential illegal voting."

Mr Stewart also urged postal voters not to allow their votes to fall into the wrong hands.

He said voters should fill in their ballot papers themselves, witnessed by someone who knew them personally. Mr Stewart said the votes should be posted as soon as possible to reach the electoral registration unit at City Hall by June 7.

They can also be handed in at polling stations in the voters' own constituencies on the day of the election or to Council offices at Keighley and Shipley or to the electoral unit at City Hall.

He added: "I would urge any voter who is asked to hand over an incomplete postal vote to refuse to do so and report the matter to the police immediately."

The letters have been sent out as balloting slips and are posted from the electoral unit to about 17,000 people who filled in application forms to vote by post.