Only Labour can be trusted to cut the cost of living.

Party strategists intend that to be the message of the party’s general election campaign in 2015. And that will be the message coming out of the party’s annual conference in Brighton, which begins this weekend.

But Labour also has a second task, and one which may be more challenging. The party needs to convince voters that Ed Miliband is the right person to be Prime Minister.

Even Mr Miliband’s supporters accept that the Labour leader has yet to convince voters that he is ready for Number 10 – although they say he is capable of doing so before polling day.

The good news for Labour is that the party has remained united since losing power in 2010, in contrast to the in-fighting that traditionally afflicted it after previous election losses,

The rift between Blairites and Brownites appears to have vanished, perhaps because the party has largely disowned and attempted to forget Mr Blair.

Ed Miliband has his rivals – such as Yvette Cooper, the Shadow Home Secretary who is seen as a potential future leader, and her husband Ed Balls, the Shadow Chancellor. But whatever distrust exists between the camps has remained behind the scenes.

So Mr Miliband is credited with presiding over a united party. At the same time, the country has fallen out of love with David Cameron, who charmed so many voters when he was Leader of the Opposition.

But as one Labour figure at Whitehall said: “The country is listening to us but it does not yet see Labour as a credible alternative Government, nor does it see Ed Miliband as a credible alternative Prime Minister.”

Labour will not attempt to write its manifesto in Brighton but it will announce a small number of concrete measures to demonstrate its commitment to improving living standards in difficult economic circumstances.

The message will be that Labour is ready and willing to make “tough” decisions and take on “vested interests”.

Particular issues to be addressed – which Labour believes will strike a chord with voters – including housing costs, energy bills and travel costs, such as rail fares.

Labour has already begun its focus on the cost of living, and last month published research which showed that, after inflation, wages are forecast to be £1,520 lower in 2015 than in 2010. This means that working people will, on average, have lost a total of £6,660 in real terms while David Cameron has been Prime Minister, so Labour says.

While the party is in no doubt that the message sill strike a chord, it is also concerned by polling which suggests voters don’t believe any of the parties are in a position to do anything about falling living standards.

Hence, the challenge will be to prove that it can make a difference. So while only a limited number of policy announcements are expected, there will be a small number of concrete measures designed to prove what type of Government Labour would be if it gained power. Examples could include measures to force developers who are “hoarding” unused land, by sitting on it until property prices rise, to make it available for housing.

And the party believes it has an enormous advantage over the Tories when it comes to dealing with people’s concerns about the cost of living, because voters don’t feel David Cameron understands the pressures ordinary people face.

Labour also believes the Government has made a serious error in claiming the economy has “turned the corner” – a phrase used by George Osborne, the Chancellor.

While the statistics may suggest that things are getting better, the day-to-day experience of many people is very different. They do not feel that their finances have improved, and to hear the Conservatives boast about progress being made only confirms the view that the Tories don’t live in the real world.

Party figures believe they can win the arguments. Their biggest challenge might be persuading people that they, and Ed Miliband specifically, are ready to govern.

One insider said: “We have a problem in terms of our credibility.

“He has a problem in terms of credibility as an alternative Prime Minister.

“On the other hand, are we capable of winning a living standards general election? Yes, because we will make a difference. We have a mountain to climb between now and 2015, but Ed is capable of climbing it.”

One question that must be on Ed Miliband’s mind is what will happen in the event of a hung Parliament.

Liberal Democrats are to make the economy their key election issue. At their conference in Glasgow, they argued that their attempts to fix the economy had worked - even though it involved making decisions which caused pain to some families (such as public sector spending cuts which led to job losses).

But the job is not yet done, according to the Lib Dems. And going back on spending discipline could put all the progress that has been made at risk, and ensure all those sacrifices were for nothing.

It’s a line of reasoning that places the Lib Dems firmly alongside the Tories and in opposition to Labour. Indeed, the implication is that Labour cannot be trusted to run the economy while the Conservatives are on the right track (although Lib Dems also argue that they blocked some of the Tories’ more extreme policies).

And yet, Liberal Democrats are also keen to stress that they could do a deal with Labour in the event of a second hung Parliament.

If Labour is the largest party and the Lib Dems hold the balance of power then they will happily speak to Mr Miliband,

Naturally, Labour will argue that it is campaigning to try to form a majority government, not to lead a second Coalition.

And many Labour activists simply loathe the Lib Dems – as they will not hesitate to make clear this week.

But when frontbenchers make their contributions to the conference – peppered with attacks on the Coalition Government – they will be aware that the Lib Dems could become their partners in power in 18 months time.