WESTMINSTER is falling apart - literally.

According to a report last week, MPs might even have to leave the Palace of Westminster for some years while it undergoes £3 billion in repairs. A fitting metaphor for the way things are going in the mother of parliaments. British politics as we have known it is being dismantled and thrown in a skip.

The old political parties are in deep trouble from the rise of incomers like Ukip in the south and the SNP in Scotland. People call it anti-politics, and it certainly is anti-establishment politics, though the parties doing the dismantling are very different in image and ideology.

Both parties are saying: we can give you your country back. The SNP offer a Scotland independent of the UK and Ukip promise an England independent of the EU. But there, of course, the similarity ends.

Ukip, under Nigel Farage, is a party that wants to curb immigration, privatise the NHS and cut spending more than the Conservatives; the SNP under Nicola Sturgeon want open borders, a publicly provided NHS and an end to austerity. But both are expressions of the same disintegration of the old politics.

The impact of Ukip has been ­devastating south of the Border. David Cameron said he would "throw the kitchen sink" at the safe seat of Rochester and Strood to humiliate Nigel Farage. But in last week's by-election, Ukip's Mark Reckless overturned a 10,000 Tory majority to win by nearly 3000 votes.

The Tories are now divided, and moving rapidly to the right on Europe in fear of losing more ­defections to Ukip, who now have two MPs and the potential to make a big impact in the General Election.

Normally, this would be good news for Labour. With Cameron moving right, Miliband theoretically has the political centre to himself - where all UK General Elections, according to opinion pollsters, are won.

But under Ed Miliband Labour seem, if anything, to be coping with the new politics even less well than the Tories. They were thrust into a humiliating third place in the by-election, with only 16% of the vote in a (renamed) seat they held until 2010.

The only consolation, perhaps, is that the Liberal Democrats returned only 349 votes and face extinction as a political force in UK politics. The Greens won five times that number of votes in Rochester.

However, Labour diverted attention from both the Liberal Democrat demise and the split in the Tory party with an extraordinary social media mishap that revealed Labour's problems over the national question in England and its own fear of Ukip.

Labour's shadow Attorney General, Emily Thornberry, resigned after she tweeted a picture of a terraced house, bedecked with Cross of St George flags, which looked like it had mated with a Transit van. This was seen as a snobbish assault on the patriotic van men and women of Rochester by a nasty Labour luvvie who lives in a £2 million mansion in Islington and is sneery about the English flag.

It was a bizarre political moment on so many levels. The tweet said nothing pejorative and was simply a picture of, well, a terraced house in a working-class area with a van in front of it. Miliband's over-­reaction revealed Labour's fear that it too is losing votes to Farage.

The Labour leader, we were told, was not just angry at the tweet, he was the "professor of angry", and he insisted later that he felt "respect" for white van persons everywhere. This only drew attention to the story, gave it legs and invited every tabloid newspaper to photograph each and every multi-million-pound home occupied by a Labour MP. Miliband's in Primrose Hill, for example.

If Thornberry had tweeted a picture of a Scottish house with a big van and lots of Saltires, she would not have been called on to resign. It would merely have been an image that confirmed what everyone knows: that many working-class people feel patriotic and/or vote SNP. Make of that what you will.

Twitter is rapidly becoming a graveyard of political ambitions. Which makes it all the more remarkable that the new First Minister, Nicola Sturgeon, announced at The Herald Politician of the Year awards - where she won the top honour - that she intended to keep tweeting in Bute House to her 100,000 followers.

The First Minister attracted the attention of the world on Friday with her new 50/50 gender-balanced Cabinet (though not of the BBC, which inexplicably failed to cover her reshuffle on the network news). Scotland, we are told, is only the third country in the world with a Cabinet that has a government with as many women in it as men. Which is astonishing if true.

So it was a bold move by the FM, and long overdue. But you could have been forgiven for thinking last week that Nicola Sturgeon had just won an election, so great was the air of triumphalism about her investiture. She hasn't actually been elected to her own job.

The chairman of Better Together, Alistair Darling, was also at the ­Politician of the Year event and looked like an also-ran, even though he had won the referendum. It was hard not to feel a little sympathy for the former chancellor. He said that everyone seemed to like him now that he had stood down.

But the extraordinary success of the SNP is not really about ­independence as such. The SNP have been buoyed by a wave of anti-establishment politics that includes many people who would never describe themselves as nationalists. The SNP would do well to remember this.

It is all about revulsion at the ­politics of Westminster, and a desire to take it out of the hands of the big parties, with their corporate connections. That's why in Scotland, anti-politics (though I don't like that phrase) is taking on such a left-wing appearance, whereas in England it has been associated with the politics of the right. Ukip reflect the anxieties of many English working-class people like Dan, the White Van Man in Rochester, who think their culture is under assault and their jobs are being taken away from them by immigrants.

But we should be wary of ­complacency in Scotland about immigration and race. Sturgeon's government is gender-balanced, but it certainly isn't balanced by race or religion or sexual orientation. One wonders how soon others will be demanding the recognition now being accorded to women in politics.

For now, though, the SNP are united, well-led and on an ­astonishing roll, with their target of 100,000 members by Christmas and polling figures that remain unread. There is every possibility that they could return more than 20 seats at the General Election

Following the Rochester and Strood by-election, Ukip are threatening to return a similar number of seats. We could have the bizarre spectacle of both Ukip and the SNP juggling the balance of power in Westminster in six months' time.

Somehow I don't think they are potential coalition partners. But the 2015 General Election is shaping up to be a real turning point in UK political history.