It’s the Nigel Farage chameleon show – flashy, ever-changing pledges, but only one real policy: xenophobia | Polly Toynbee

If you screw up your eyes and look four years into the future, can you imagine a Prime Minister Farage standing victorious on that No 10 doorstep? I’m afraid the answer is yes – just about. I can see that ghastly grin. If everything that can go wrong does go wrong, then it’s not inconceivable, and everyone had better believe it.

The showman had on his serious face to talk about the economy in today’s speech. He had some pretty heavy lifting to do, heaving out impossible promises made only a short time ago. Gone was his £90bn tax cut bonanza. Public spending will be slashed instead: Reform has already put 100,000 civil servants “on notice”. Farage the chameleon now says his is both “the party of workers” and one that is “pro-business”. Reform had also briefly posed as the party of poor children with a suggestion that it would end the two-child benefit cap, but Farage rapidly cut back eligibility: now it’s only for couples, only when both work, and only for British nationals. He also promised spending cuts and big cuts to the benefits bill.

His mercurial shapeshifting comes under a little more scrutiny now he tops the polls, but not much. His will be the greatest party of “risk-takers”, plunging the country into crypto like Donald Trump. (Might he, too, launch his own token?) With undisguised glee he predicts an economic collapse in 2027, forcing an election to sweep him to power. He mentions “a self-induced act of financial stupidity”. At last! Among all his backflips and reversions, is this the confession we deserve from the man who instigated the great Brexit calamity? No, of course not. He is talking about the non-dom tax he would remove to lure back wealthy expats, including some of the quarter of a million Britons now in Dubai.

On Brexit, since the popular mood has turned against it, all we get is a grumble that others have “squandered” the opportunity it provided to reduce regulation. Expect nothing on the thousands of extra civil servants hired to replicate tasks done in Brussels. Nothing either on £80bn in tax revenues lost annually due to Brexit, a costly price for “sovereignty”. How absurdly he poses as the friend of Brexit-stricken business. Labour has, at last, taken off its self-imposed gag about Brexit. It needs to hammer home the damage this man did to the economy.

The only reason we listen to Farage, and the only reason he tops the polls, is his prowess in pumping animosity towards immigrants to the top of the political agenda. This one-man band has only his xenophobic dog whistle to signal his party’s course into government, the same one sweeping the right in across the democratic world. Without that, who would care about his views on anything else? He has pledged “net zero migration”. In a deeply angry country, other sources of discontent may well fill his sails, but however hard he tried to promote other policies today, immigration is his only proven winner. As he takes up the mantle of the next popular issue, he buries his own perverse political predilections: his choice of Putin as his most admired leader, his fondness for Trump, and his frequent calls to replace the NHS with private health insurance. Despite all this, his only calling card with voters is a toxic loathing for foreigners.

He may have reached his peak. The political scientist John Curtice tells me that having scooped up older, socially conservative voters, Farage is less popular among the young, especially female voters, who are “almost all socially liberal on diversity, graduates and non-graduates alike”. Nor will Reform’s record in its 10 county councils back up Farage’s national promises of vast efficiency.

Farage answered every question after his speech, except one. The Guardian asked if he still adheres to his lifelong support for proportional representation. Silence. It’s become clear recently he has changed his mind, now that our wildly distorting first-past-the-post (FPTP) system is his only path to power. FPTP is becoming his “friend”, he recently told Sky News Australia.

Shamefully, there is silence from Labour on this, too, despite majority support for electoral reform. If Farage should win, it will not be because of any image transformation, but because Labour’s failure to reform our electoral system would give Reform victory on just over a quarter of the vote. That, after all, is why PM Farage is in any way imaginable.

• Polly Toynbee is a Guardian columnist