By Chaminda Jayanetti

The publication of Labour's manifesto comes as a relief. It has actual policies - truckloads of them, across every area of government activity. It has costings, or at least attempts at them. It breaks completely with the Thatcher-Blair-Cameron economic consensus, sparking some electricity in this campaign's soporific proceedings. It gives us something concrete to talk about, at last.

But let's be clear - while the policies deserve serious consideration and scrutiny, it is highly unlikely Jeremy Corbyn will be prime minister on June 9th. The boldness of Labour's vision makes it an interesting exercise, and respect for the voters demands that they be analysed, but these policies will not be implemented by the government from June unless Theresa May decides to adopt them.

There is an election, however, where these policies will be central - the almost inevitable leadership election that will follow the public vote, regardless of whether Corbyn fights or quits.

The popularity of some of these policies in opinion polling - high public support for renationalising the railways, banning zero hours contracts and taxing the rich - means that many Labour members will mostly blame electoral defeat on Corbyn's unpopularity.

As a result, they are likely to demand that candidates to replace him as leader commit to keeping his policy agenda, or at least specific parts of it.

That's not an illogical demand - if the policies are popular but the leader is not, why change the former as well as the latter?

But this will put centrist candidates - Yvette, that's you - in a difficult position. Labour's centrists believe, not without foundation, that while individual spending pledges and tax rises might poll well, taken together they reinforce Labour as a party that is "extreme", "risky", and "too left wing", to use the sort of phrases directed at it in focus groups. People like sugar and people like honey, but have them together and it all gets sickly sweet.

It is easy to envisage a campaign where Cooper - or Chuka Umunna, Lisa Nandy, or whatever other non-Corbynite runs - gets peppered with questions about every single point of the Corbyn manifesto. Will you axe tuition fees? Will you tax the rich? Will you create a National Education Service? Will you renationalise rail and water? Any departure from one of these policies will seem like apostasy. To depart from positions that are both popular and genuinely left-wing will hand the initiative to the Corbynite candidate - or Corbyn himself.

The manifesto itself is not a programme for government. Thursday's leak contained no mention of water renationalisation - and yet come Tuesday, it has suddenly appeared. That would suggest that in the space of just five days, the Labour leadership decided to commit to a major renationalisation of a key public utility. They haven't yet worked out how to go about it, which provides little evidence that this has been entirely thought through.

Bear in mind also that Brexit will be a huge drain on the capacity of the civil service and the state over the next five years. Labour is effectively saying that Britain's civil servants will be able to renationalise the railways, water utilities, the National Grid, Royal Mail, create regional public energy companies, a National Education Service and a National Care Service, create a large National Investment Bank and regional development banks, build a million homes and abolish tuition fees - to name just a few - at the same time as managing Brexit negotiations and their fallout.

That's bonkers.

This is not a programme for government - not for the next five years, at least. It is a bold statement of policies and policy direction - made, in some cases, in something of a rush, but with the intention of establishing a new policy baseline for the Labour party. In this task it may well succeed.

Conservatives will no doubt be glorying in their huge poll leads and bringing out tired mantras about 1983 and the 1970s. But for the first time in decades, taxing the rich, renationalising utilities, and creating traditional state-run universal services are in a mainstream party manifesto and across the evening news. Even the Conservatives are now looking to build more council housing.

These are no longer fantasies - no matter how fanciful you may find them and their costings, they are now part of Britain's political spectrum. Most people agree with certain policies. A substantive minority agrees with most of them. They are no longer at the margins. Blairites can't put this back in its box.

And if the Tories fail in power, they may find this new political agenda is next in line.

Chaminda Jayanetti is covering the general election for Politics.co.uk. He tweets here.

The opinions in politics.co.uk's Comment and Analysis section are those of the author and are no reflection of the views of the website or its owners.