Labour has extended its poll lead to four points but just one in five people can imagine Ed Miliband as prime minister, according to a poll.

The survey put Labour on 34%, unchanged from last month despite infighting within the opposition ranks and speculation about Miliband’s leadership, with the Tories down one point on 30%.

The ComRes study for the Sunday Mirror and Independent on Sunday put Ukip on 19%, the Liberal Democrats up one point on 8% and the Green Party down one point on 3%.

The proportion of people who said they could imagine Miliband in No 10 has fallen to 20%, down from 25% 12 months ago, with those disagreeing up six points on 59%.

Only 50% of Labour voters said they could imagine Miliband as prime minister, a fall of nine points compared to November 2013.

Almost a quarter (24%) of Lib Dem voters said they could imagine Miliband in No 10.

Only 29% of those asked trusted Miliband to stand up for working people, compared with 22% for David Cameron.

And half of those surveyed expect Cameron to make deep cuts to public services if he is in No 10 after the 2015 election, compared with 24% for Miliband.

ComRes interviewed 2,000 British adults online between November 12 and 14. Data was weighted to be demographically representative of all British adults and by past vote recall.