Ed Miliband is facing mounting pressure over his leadership after latest poll ratings revealed most voters do not view him as a prime minister in waiting.

Research for The Times found fewer than one in five adults, just 19%, could imagine the Labour leader in No 10, putting him significantly behind Prime Minister David Cameron when he was in opposition.

The YouGov poll found that only 26% of voters think Labour is ready for government, while among the party's supporters fewer than half, 49%, believe Mr Miliband looks like the country's next premier.

It comes after f ormer minister David Lammy became the latest senior Labour figure to speak out, warning the party had become overly focused on the issue of living standards without spelling out its "positive offer" for people to vote for them.

One of the party's biggest donors, businessman John Mills, said Labour had become "boxed in" on the economy with a strategy that differed little from the Conservatives.

Mr Miliband's leadership has been questioned after his failure to respond directly to measures in last week's Budget was seen to have handed the Tories a political victory. Weekend opinion polls showed the two main parties effectively on level-pegging.

Mr Lammy said that, with 14 months to the general election, Labour was in danger of being drawn into a fight on the Conservatives' ground.

"Effectively we knock on doors and the central message is about living standards and energy prices," he told BBC Radio 4's The World at One yesterday.

"I think the electorate will need more in a raft of areas and we need to be very careful that we are not solely fighting the election on the current Government's ground which is deficit reduction and a debate around welfare and immigration. There is more to fix in this country than just on that sole platform."

He said that Mr Miliband needed to be able to inspire voters and to demonstrate that Labour was ready for a return to office.

"We have to spell out to the country what our positive offer is for them to vote for us. That has to connect, it has to be relevant, it has to inspire and motivate," he said.

"I think we have been a very effective opposition but in the next 14 months we have to cross that Rubicon to being a government-in-waiting. I think that has yet to happen."

A group of influential left-leaning thinkers joined forces earlier this week to urge Mr Miliband to produce "transformative" policies that would excite voters and not rely on Conservative unpopularity to secure a return to government.