NIGEL Farage, never short of a glib excuse, assures us that Ukip has only "a handful" of potentially embarrassing candidates lined up for tomorrow's English local elections.

It makes for an interesting question if you lead a party aiming for power and influence.

How many staunch patriots do you need giving Nazi salutes, making racist and homophobic comments, or holding unpleasant opinions about the Holocaust before the threshold of unease is crossed and you start to wonder about the company you keep?

As it turns out, the party that Ken Clarke, Minister Without Portfolio, dismisses as an alliance of "fruitcakes, loonies, waifs and strays" – mostly former Tories strangely enough – also has only a handful of policies. As a leaked exchange of emails among the leadership revealed at the weekend, persuading any two members to agree about anything apart from immigration and Europe has proved difficult. Fruitcakes come in many varieties.

As things stand, nevertheless, a party with no credible programme, one represented by some people who think – to take just one example – that physical exercise "prevents" homosexuality, could win big in English local government. Buoyed by the sort of donations that used to go to the Tories, Ukip has spent £200,000 on advertising and means to field 1732 candidates.

This suggests, first, that there are many more "fruitcakes, loonies, waifs and strays" around than Mr Clarke or anyone else has perhaps realised. The fact that support is converging on Ukip both from the Conservatives and from erstwhile fans of the BNP is also illuminating. If the lure is nothing better, in the absence of other policies, than a dislike of immigration and immigrants, a disturbing picture emerges.

In 2006, David Cameron was as disobliging as Mr Clarke in describing the psychological condition of Ukip supporters, but the then leader of the opposition went further. He also called them closet racists "mostly". Yet the same Mr Cameron now lives with the uneasy knowledge that such individuals could cost him several county councils and the next General Election.

Mr Farage might be right when he claims that a rapidly growing party has been unable to vet every candidate. It's also possible that Ukip has fallen victim to the kind of entryism that used to be Labour's problem. But the party's only high-profile figure forgets to ask why his right-wing insurgency is proving quite so attractive to former BNP members, or why his rhetoric is preferred to that of a distinctly illiberal Tory Party.

The fact remains that Ukip has ceased to be a fringe phenomenon. Mr Farage has no hope of an invitation to Downing Street and his party's chances of actually winning Commons seats are probably remote. But he is very close to achieving a position of influence over the Conservatives. It was perfectly clear after the Eastleigh by-election that plenty of Tory back-benchers are not-so-secret Ukip sympathisers. Starting on Friday morning, those people will make themselves heard.

If this was just Mr Cameron's problem, we could all sleep more easily. If all that Mr Farage's faction succeeded in achieving was a split in the right-wing vote that put the Tories out of the office, the fruitcakes would have done us all a favour. That's not the nature of English politics.

Ed Miliband has already added immigration to his growing list of the "mistakes" made by Labour while in government. Nick Clegg has abandoned LibDem plans for an amnesty aimed at illegal migrants and suggested, instead, that some of those coming into the country – just some, mind you – should lodge "security bonds" of £1000. On this, as in so much else, the drift to the right by the Westminster parties is unmistakeable.

Mr Farage shouldn't get all the credit. Certain newspapers have been working for years to give xenophobia political credibility. But Labour and the Liberal Democrats have clearly been getting the same results from their private polling as the Tories. In parts of England, it seems, there is no such thing as an extremist immigration policy. In this squalid game a politician cannot be "tough" enough.

Ukip has no leverage in Scotland. That's reassuring, but no reason for self-satisfaction. The party's tendency to confuse England with the UK while demanding the abolition of the Scottish Parliament does it no favours. That doesn't mean it's anti-immigrant rhetoric would have no appeal in these parts. Intolerance always finds an audience in the end.

It would be foolish, therefore, to dismiss some English local elections as irrelevant. It would be unwise, too, just to hope for a dividing of the right-wing vote. Mr Cameron will pander to the Ukip and its supporters if he thinks it necessary. Labour and the Lib Dems will not be far behind. This will affect Scottish politics both indirectly and directly.

It amplifies a point made the other day by my colleague Harry Reid. A No vote in the independence referendum is no guarantee of political stability or an end to the constitutional arguments. But where would we stand, as a political community, if we decided to stay in a United Kingdom in which a Conservative government was being maintained in office by the likes of Mr Farage?

His arguments, if they deserve the name, are being conceded on every side. You could mock Ukip, as Mr Clarke mocked it, for being nothing better than a party of protest, "a collection of clowns or indignant, angry people". But the Minister's fighting talk has been met with an ominous silence on his own side. The depth and extent of anger in England's cities and shires, rational or otherwise, is being accepted as a political fact. If – when – the Tories lose badly tomorrow, Mr Farage will have some real power.

Immigration has been a running sore in British politics for decades. Forty-five years ago, Enoch Powell was sacked for an infamous attempt to exploit the issue. Rhetorical flourishes aside, his speech would scarcely raise an eyebrow today. What once was the politics of the fringe is now the politics of the mainstream.

When the last of English local election results are counted, we might pause to ask ourselves if we want any part of that.