If the telephone rings at 7pm tonight don�t answer: it is bound to be Nick Clegg, the leader of the Liberal Democrats, calling for your opinion on tax, the economy, crime or the environment.

If the telephone rings at 7pm tonight don't answer: it is bound to be Nick Clegg, the leader of the Liberal Democrats, calling for your opinion on tax, the economy, crime or the environment. If you approve of his 4p tax-cut plan you may be asked to press button one, if you want electoral reform press two, to scrap the council tax press three.

More than 250,000 households across Britain are due to have their evening disturbed by an automated cold call from Mr Clegg in an attempt by the LibDems to "connect" with people that has the potential to backfire badly.

Immediately after coverage of the leader's speech is broadcast on the evening news tonight the party aims to press the button on an automated dialling system that cold-calls voters in 50 key constituencies with a pre-recorded message from the leader.

The taped voice of Mr Clegg will introduce himself and ask listeners to respond to a series of statements on LibDem policies, marking their approval with the button keys on their telephone.

Party strategists are convinced that the tele-marketing approach, a byword for annoyance at children's bathtime, is the future of politics. But the new tactic, imported from the Democrats in the US, cut the legs from a preview of Mr Clegg's speech to the conference today.

Party managers had hoped that the novel approach to campaigning would be a hit with the media and voters but it was immediately spotted as a presentational own goal.

In a pilot of the system calling 10,000 voters in the south-west of England, using Paddy Ashdown's voice, had proved a success with 50% of callers not slamming the phone down immediately.

"The evidence shows that people do take these calls, people do want to express their opinions and we do get very interesting information and feedback from the process," said Danny Alexander MP, chief of staff to Nick Clegg.

The Liberal Democrats claimed it was the first time the polling had been used in the UK. If rival parties have undertaken similar exercises they have kept quiet about it because they ridiculed the idea.

"This is not just a nuisance call, it shows how screamingly out of touch the LibDems are," said Stephen Pound MP, a Labour scourge of the LidDems. "Nick Clegg will probably dial the wrong number and if Vince Cable has anything to do with it he will probably reverse the charges."

Mr Clegg compounded the situation in an interview with regional television when he estimated the state pension was "about £30 a week". The pension, introduced by Liberals in 1908 when Lloyd George was chancellor, is in fact at least £90.70 a week or £145.45 for couples.

The blunder, worse for a politician than not knowing the price of pint of milk, undermined the man-in-touch image Mr Clegg has been nurturing.

Pensions Minister Mike O'Brien accused Mr Clegg of living in an ivory tower. "This just shows how out of touch Nick Clegg is with the lives of ordinary pensioners," said Mr O Brien.

In his speech today Mr Clegg will attempt to regain some of the ground he lost during the week by hammering home the point that his is the party of low taxes and social justice - triangulating both Labour and Tory rivals.

He will claim that British politics has changed forever and that the Labour Party, self-destructing under Gordon Brown, is finished. "The Liberal Democrats are the only party that can deliver social justice," Mr Clegg will say. "We are the only choice for anyone who wants a fairer Britain."

Mr Clegg will also make play of the planned 4p tax cut approved by conference this week and plans to close tax loopholes which gives him the flexibility to outflank the Conservatives on their traditional territory.

"I want this to be the most progressive - most redistributive - tax plan ever put forward by a political party," Mr Clegg will say. "My aim is to cut taxes so that nine out of 10 British taxpayers are better off."

He will also promise to "connect with people" as he has done in regular town hall meetings during his nine months as leader, by urging LibDem activists to knock on one million doors between now and the European elections in June. Before people answer the door, though, many of them will have to deal with a nuisance caller.