Ed Miliband must put substance on his slogans and indicate how the country will change if he is to win the next election, Mr Clarke has said,

The Blairite warned the party must not make the same mistakes of 2010 when it failed to justify another 13 years in office. He said: 'My view is you will not win the 2015 general election on a slogan or set of slogans. We will only win if we put substance underneath it and indicate how the country would change if Labour was elected and we really go out and deal with that. That is not about assembling a collection of negatives – 'we wouldn't do this, that or the other'. It is about collecting positives and I don't think we have done that.'

He added: 'I think the main reason we lost the 2010 election was there wasn't clarity about what we would do as a government. We absolutely can't fall into the same trap this time.'

He described Norwich as the 'acid test' of what the Labour Party had to be to be successful in British politics. The two prospective Labour candidates, Clive Lewis in Norwich South and Jessica Asato in Norwich North, were both 'full of ideas and thoughts', he said, but they could only get so far as individual party candidates. He also questioned the approach of shadow chancellor Ed Balls who he said had 'developed the doctrine of never making a commitment to anything ever at any time other than to support Norwich City Football Club'.

'Actually that is no good. It means the front benches, shadow cabinet members, do not always feel able to go out and say their thoughts because the economic dimension to whatever you are saying is important. If you don't have the support and agreement of the shadow chancellor in advance that makes it difficult.'

He described Mr Miliband's efforts to build a coalition of people, ideas and thoughts to give a choice to the people of the country and set out a future for the people of the country as a 'work in progress', and also urged him to set out policies.

'People say you should not show too much before a general election, I don't agree with that approach. If you policy is substantial and has weight, it will stand for itself and if others agree with you and the government agrees with you then that is fine.

'I don't think politics is about dividing lines and the difference between us and everybody else. Politics is saying what we would do.'