The BBC filled more than half its election TV debate audience with left-leaning voters, some of whom were brought in from Scotland and Wales, it emerged last night.

The audience at the filming of Thursday night’s debate in Westminster repeatedly cheered calls for more public spending and strong defences of immigration.

When Ukip leader Nigel Farage interjected and said they were prejudiced, ‘even by the Left-wing standards of the BBC’, the audience only booed him further.

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Bias: When Ukip leader Nigel Farage (right) said the audience was prejudiced, they only booed him further

David Dimbleby, who hosted Thursday night’s debate between the Labour, Ukip, Green, SNP and Plaid Cymru leaders, pointed out that the audience had not been selected by the BBC, but by a ‘reputable polling organisation’, later to be revealed to be ICM.

The BBC initially refused to disclose the political make-up of the audience but eventually released figures late yesterday. Of the 200-strong audience, about 58 were Conservative or Ukip supporters while about 102 backed left-leaning parties – Labour, the Lib Dems, SNP, Plaid Cymru or the SNP. The rest – 40 – described themselves as undecided.

The figures mean just 36 per cent of the audience members with a declared political allegiance were supporters of the Tories or Ukip. But the latest ICM poll for the Guardian put the Tories on 39 per cent and Ukip on 7 per cent – a total of 46 per cent overall.

Last night Mr Farage said: ‘If the audience make-up didn’t reflect that then it’s wrong.’

Out in the cold: Ukip leader Nigel Farage cuts a isolated figure at the end of the BBC TV debate on Thursday

The BBC told ICM to make sure a fifth were so-called floating voters, and for every five Labour supporters in the room, it made sure there were five for the Conservatives, four for the Lib Dems, two for the Scottish National Party, two for the Green Party and one for Plaid Cymru.

The figures suggest supporters of the Tories and Ukip were significantly under-represented.

ICM admitted that it recruited almost all of its audience members London.

The company said in a statement that it identified ‘30 small geographical areas’ within a 20-mile radius of the Westminster debate hall and found at least eight people from each one.

It also selected a ‘small number’ of SNP and Plaid Cymru from Scotland and Wales using an undisclosed method ‘reasonably decided upon by ICM’.

The company refused to answer any other questions about the matter.

Yesterday the BBC refused to disclose how many people had complained about its broadcast.

‘Our data shows the number of audience contacts were heavily influenced by the issue being raised during the debate and therefore we won’t be giving out figures,’ a BBC spokesman said.

Conservative MP Andrew Percy said: ‘The audience should reflect the opinion polls and the fact is that nearly half of the country say they would vote Conservative of Ukip,’

‘You have to ask yourself what would have happened if the audience had been right of centre. The left would have had a field day. They would have been so holier-than-thou.’

John Hemming, Liberal Democrat MP for Birmingham Yardley, said the BBC’s behaviour was ‘ludicrous’ and its refusal to publish the number of complaints ‘added insult to injury’.