DURING a trip to Westminster, everyone I spoke to tried to calculate how destructive the electoral earthquake would be after this week’s European election.

The result seems inevitable. Nigel Farage’s Brexit Party will be the ‘winner’, regardless of vote share, the Lib Dems and Greens will enjoy a successful night, while Labour and Tories will incur the wrath of voters.

Conservative supporters will punish the Prime Minister for not securing a deal to leave the European Union. Labour voters will desert Jeremy Corbyn for not doing more to oppose Brexit. The image of the night will be a grinning Farage.

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Protest votes provide an opportunity in the mid-term to issue a warning to the Government of the day, but this poll feels different. Voters will use this election to reject Westminster’s political class.

It is not hard to see how this crisis could play out south of the border. Despite a victory for the Brexit Party, which will give momentum to a ‘clean break’ from the EU, May will be unable to push through any withdrawal agreement. Angry voters will become livid.

Farage will say that this Parliament is unable to deliver on the will of the people. He will persuade some Tories who are part of the European Research Group to become Brexit Party MPs. Against a backdrop of impressive general election poll ratings, this new political outfit could support a no confidence motion in May's Government. After that, pandemonium.

Even political progressives concede that the Brexit Party is, unlike UKIP, an impressive and effective organisation. Armed with a clear political message, and bolstered by professional social media content, Farage’s team is on the rise. He is stirring a cocktail of betrayal and treachery, and it is working.

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In Scotland, the result is likely to be no less dramatic. The SNP will win comfortably, and the Brexit Party will perform well. Again, watch out for the Greens and a mini-revival from the Lib Dems.

The story of the night north of the border, as it will be across the UK, will be on how low the Labour and Conservative vote shares have fallen. One poll last week had the Scottish Tories trailing the Greens, while Scottish Labour languished on 6%.

The low poll rating for Ruth Davidson’s party was inevitable. She wanted May’s Brexit deal to be ratified by MPs and she tied herself politically to the Prime Minister. It was a gamble - an understandable one - and her party will be punished.

Scottish Labour leader Richard Leonard, by contrast, has volunteered for an electoral drubbing. Given that his party is on the majority side in Scotland on Brexit, arguing for Remain would have been popular electorally. He instead chose to echo the convoluted and confusing Brexit line handed to him by Corbyn. Leonard has asked voters to slap him in the face.

However, pundits should be cautious about using the looming European result to make predictions about the Holyrood election in 2021. If a week is a long time in politics, twenty-four months feels like a lifetime.

Rewind the political clock back two years and look where we stood. The SNP lost around twenty seats at the general election and was on the electoral downslope. Davidson’s party recorded its best result in decades. And Scottish Labour jumped from one seat to seven. The electorate was, and is, volatile.

The period between Sunday - when we will know the result - and the next Holyrood campaign is marked by “known unknowns”. Brexit may be resolved within months. Or not. The Tories could have a new leader who reinvigorates the party. Or they may pick another dud. Davidson is at the mercy of events she can barely control.

The SNP’s prospects are just as hard to predict. It is extraordinary that a party that has been in Government for twelve years is still routing the opposition in elections. Nicola Sturgeon’s record on public services is poor, but the SNP can nonetheless present themselves as the change option through independence.

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But senior Nationalists are cautious rather than complacent. A potential trial involving former SNP leader Alex Salmond may be a speck on the horizon, but the party hierarchy cannot take their eyes off the skyline. I cannot over-estimate how nervous SNP figures are about the potential effect on the Yes movement of the Salmond charges.

It is also impossible to forecast what will happen to the dwindling, warring tribe otherwise known as Scottish Labour. Leonard has struggled, but so did Corbyn in his early days. He does not have control of his parliamentary group, but the same was true of his bearded ally and he survived. Leonard needs to raise his profile and change the conversation. Unlikely, but not impossible.

We will reach the cross-roads in May 2021 and be faced with one question. Will the two independence-supporting parties - the SNP and Greens - win a parliamentary majority for requesting indyref2? Until that question is resolved, Scottish politics will always be in a state of flux.