Police investigating allegations of postal voting fraud this morning made a second arrest, as candidates gave warning of a rash of legal challenges to general election results.

The arrest of a 38-year-old-man in Bradford yesterday came after The Times revealed evidence of potential vote-rigging in the city. A second suspect, aged 51, was detained this morning. Detectives say they expect to make more arrests in the coming week.

West Yorkshire detectives launched their investigation last week after The Times highlighted concerns about the number of voters registered at the home of a Conservative councillor, Jamshed Khan, and at a second, derelict address in the city.

Mr Khan, 51, a councillor in a Labour-held marginal Parliamentary seat, insisted that he had done nothing wrong and said he would be “seeking legal advice” over the allegations. He resigned the Tory whip while the investigation was continuing.

As more postal ballot blunders have been disclosed it has become clear that thousands of voters risk being disenfranchised because they have not received the correct papers.

A record 6.5 million people are expected to vote by post, nearly four times the number in 2001, and almost a quarter of 26.4 million total who voted then. A survey of London boroughs showed even bigger increases in some constituencies. In Hackney, East London, which covers two parliamentary seats, the number of postal votes has jumped from about 2,000 in 2001 to 37,000.

The Royal Mail had advised people to send in postal votes by yesterday at the latest but those who receive their ballot paper before polling day can deliver it by hand up until 10pm tomorrow. The Royal Mail refused last night to accept responsibility for any delays and said that it had delivered every item received from returning officers.

Fears that problems with postal voting might blemish the election resurfaced as Labour broke with convention and risked accusations of jumping the gun by laying out detailed legislative plans, including eight Bills, for a third term.

Labour’s confidence about tomorrow’s result came as the latest poll for The Times showed the Conservatives worse placed than before their record defeats in 1997 and 2001. The final Times/ITV News tracker poll, by Populus, puts the Tories on 27 per cent, down 2 points on yesterday and by far their worst figure of the campaign.

Labour is unchanged on 41 per cent, with the Liberal Democrats up 2 points on 23 per cent, their highest of the campaign. The Times will produce a new poll predicting the result for tomorrow’s paper.

The figures comes amid signs that many senior Conservatives are unhappy about the conduct of their campaign. Several contacted by The Times yesterday said that the policy of shoring up the core vote appeared not to have worked.

Michael Howard is under pressure to remain leader even if Labour wins comfortably. Some MPs want him to stay on for a year while the party recovers, analyses the way forward and chooses a successor.

Both Kenneth Clarke, the former Chancellor, and William Hague, the former leader, publicly urged Mr Howard to stay on to help the party to kick the habit of snap leadership elections. But it was predicted last night that recriminations would follow over the weekend if the polls are right.

Meanwhile candidates in Hereford, a Tory target, gave warning of a legal challenge if the result is close, after big delays in sending out postal ballot papers. Paul Keetch, the Liberal Democrat candidate who is defending a 968 majority, said that hundreds of ballot papers had still not turned up or were sent out after people had gone on holiday.

“If the result is close, Herefordshire council may well face a legal challenge to the outcome of this election,” Mr Keetch said. Residents in Hereford have been asked to collect their ballot papers from Leominster — in some cases an 80-mile return journey — if they want to vote.

In Havant, Hampshire, voters were sent ballot papers for the parliamentary election which said: “Do not vote for more than two candidates.” Ballots will be void if people vote for more than one candidate.

In Michael Meacher’s Oldham West and Royston constituency, more than 2,500 duplicate postal votes were printed and sent out a week after the originals were dispatched. The duplicates were posted by the printers without informing election officials.

In Macclesfield and Tatton, more than 2,000 postal votes have failed to arrive and the acting returning officer has ordered a reissue. Some of the duplicate packs were delivered by hand yesterday but some householders admitted that they had received two.

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