It should be a walkover. The Conservatives are 20 points ahead in the opinion polls. Labour is at war with itself and led by an amiable no-hoper with the leadership qualities of a garden shed. The SNP have nowhere to go but down from the 2015 tsunami, and the Liberal Democrats are simply nowhere.

The Electoral Calculus website forecasts a Tory victory in the June election of 112, which sounds, on historical trends, optimistic...for Labour. The last time they were this far behind, in 1983, Margaret Thatcher won a 144-seat majority. There's no need for a suicide note now.

So what could possibly go wrong? Well, there are a number of minor flies in the Tory ointment which are worth mentioning, and not only in Scotland where the Tories may well be wiped out (again) by losing their only MP, David Mundell who has a majority of just 798.

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First of all, there is, on the Prime Minister's own terms, no justification for this general election. “Now is not the time” she says on the calls for a second referendum on Scottish independence for, so why is it time for this? In her Downing Street statement yesterday, Mrs May said: “The country is coming together but Westminster is not.” In fact, it is the other way round. The country is far from united: almost half voted against Brexit in June, and Scotland, Wales and Northern Ireland are in open revolt.

Meanwhile, Mrs May has consistently got her way in Westminster, winning the Article 50 vote by an overwhelming majority. Labour is offering only token resistance and the Liberal Democrats with only eight MPs are too small to matter. The House of Lords has also accepted the government has an unchallengeable mandate and has not sought to impede Brexit in any significant measure. The Supreme Court ruled the Scottish Parliament had no legal right to interfere.

So, why is Mrs May forcing the country into an election when she has a comfortable working majority and hasn't lost any significant vote? Did the PM not say repeatedly she intended to run until 2020? What has changed? A cynic might well say it has finally dawned on the UK Government that the Brexit negotiations are going to be very difficult. The EU is not going to roll over and give Britain free and “frictionless” access to their internal market. Mrs May is cutting and running; getting a vote in before the reality of hard Brexit hits home.

The Fixed Term Parliament Act was passed by a Tory-led government in 2010 with the express intention of preventing headstrong prime ministers doing what Mrs May has just done: call a general election despite having lost no key votes in parliament simply to boost her own majority by taking advantage of the disarray in the Opposition. At the very least, it is not how we are supposed to do things these days.

In these volatile political times it is very unwise to take electorates for granted, as David Cameron discovered over Brexit. Political attitudes can turn on an electoral sixpence. Parties can come from nowhere. The French presidential elections have seen several remarkable about turns, including the recent rise from nowhere of the far left candidate, Jean Luc Melenchon.

By no means all of Mrs May's policies are popular – especially among the poorer English “left behind” voters who are supposed to be the bedrock of Brexit. They may have rebelled in the north of England in June 2016 and voted to leave the EU to register their discontent at losing their jobs (or so many thought) to foreigners. But they are quite capable of changing back to Labour, especially since they now realise Brexit is not going to bring those jobs back or (whisper it) even reduce immigration very much.

Since June they have had time to reflect on whether the low tax, low regulation vision of Brexit presented by the Conservatives is really what they had in mind. Inflation is returning with a vengeance, with energy and food prices squeezing living standards. Meanwhile, Labour is saying clearly they will not reverse Brexit and Ukip is a busted flush

If Labour were to stop fighting amongst themselves for ten minutes they could put together an attractive manifesto; £10 minimum wage, free school meals, restoring the 50p tax band, investment bank, ending charitable status for private schools. Jeremy Corbyn's policies, even “lefty” ones like rail renationalisation, are actually rather popular. Mrs May's policies, like grammar schools in England, are not.

Labour's main problem is Mr Corbyn. He has a very poor public profile, not helped by the fact the majority of his MPs have no confidence in him. But even this is not beyond remedy. Mr Corbyn has restored Labour as a mass membership party. A concerted campaign by prominent Labour figures to support him, stressing Labour is about more than any one individual, could make a difference.

The Tory victory in 2015 was partly based on the collapse of the Liberal Democrats who lost 50 seats. If they revived, and Labour held onto its core seats, Mrs May could have a fight on her hands. Tactical voting could be a big factor since many will be voting on an anyone-but-Brexit ticket. In Scotland the SNP are on course to return well over 50 seats themselves.

Of course these are very big “ifs” and, for the record, I am not forecasting a Conservative defeat. All the evidence points to Mrs May being returned with a large majority. But this doesn't mean there is nothing for the opposition parties to play for. We are living in the age of fluid, non-aligned populist politics.

There is an arrogance about Mrs May, a sense of entitlement to “her mandate” that makes this general election seem like her attempt to rig her own popularity contest. British voters don't like leaders who get above themselves. This general election should never have been called and Mrs May doesn't deserve to win it.