Nobody believes Theresa May is in it 'for the long term' – and that's a very frightening prospect

It is an open secret that the prime minister will not lead her party into another general election, but with an influx of right-wingers the Conservatives after May risk turning into a Trump-lite gaggle of Little Englanders

Theresa May is enjoying some rare positive media coverage of her trade mission to Africa, but cannot escape the Brexit nightmare that will greet her on her return. Asked about the threat of a leadership challenge, she insisted: “I’m in this for the long term.”

If she had said anything else, she would have provoked another wave of speculation about her departure. She has to pretend she is going on forever until she is not; when Tony Blair pre-announced his departure, his authority drained immediately.

But it is an open secret that May will not lead her party into another general election. Even her allies now admit it. If she survives moves by hardline Eurosceptics to depose her this autumn and takes the UK out of the EU next March, that would be a very dangerous moment for her. She would come under enormous pressure to disclose her departure timetable, and to pre-empt attempts to oust her by making a dignified exit.

The knowledge that a leadership contest to choose May’s successor is coming has prompted a campaign by Nigel Farage’s lieutenants to flood the Conservative Party. People who have been members for three months can vote in leadership elections. Tory MPs choose a shortlist of two in a series of ballots, from which Tory members would elect our next prime minister.

An increase on the most recent 124,000 membership figure is likely to be announced at next month’s Tory conference. Normally, that would be good news. While Tory HQ will doubtless claim the rise is due to its membership drive, the truth is probably more sinister. Realising that Ukip is a busted flush and has served its purpose, Ukippers are infiltrating the Tory party. Some Tories don’t mind: they point out that many recruits are “re-treads” who left the Tories for Ukip and are now happy to return to “the party of Brexit”.

Although Arron Banks, co-founder of Leave.EU, and his adviser, Andy Wigmore, have had their Tory membership applications blocked, it will be impossible for the party to veto ordinary ex-Ukippers. Banks has urged Leave.EU’s 90,000 members to join the Tories to unseat May and “help install a true Brexiteer such as Boris Johnson or Jacob Rees-Mogg to the top job”. Pro-EU Tory MPs are rightly alarmed by Banks’s pledge to recruit new members “hopefully in areas where the party has extreme ‘remain’ MPs”. Some have already seen a membership surge in their constituency. The implied threat is that they could be deselected if they don’t toe the line on Brexit.

The move, dubbed “Blue Momentum”, carries huge dangers for the Tories and could turn into the “Purple Peril”, as Ukip was once called. Of course parties must be open to new members, but the Tories hardly need an influx of more right-wing, Eurosceptic ageing men. Only 30 per cent of Tory members are women, down from 49 per cent in 1994. Ukip’s imbalance is even worse; women account for only 25 per cent of its members.

There is no future for the Tories as a party of power unless it appeals to the under-50s and ethnic minorities. Their support among these voters fell at last year’s general election; these groups are the future.

A study by the bright, new, modernising, centre-right think tank Onward calculates that the growing BAME population, and a 6 per cent fall in the white population by 2031, means the Tories will lose a swathe of seats unless they achieve a 2 per cent swing among white voters or 12 per cent swing among ethnic minorities. When the proportion of BAME voters grows to 10 per cent in a constituency, it is more likely to be Labour than Tory. Once the BAME vote reaches 30 per cent, the Tories can’t win it, Onward warns.

Tory modernisers fear the party has a massive problem and are worried that David Cameron’s efforts to woo the ethnic minority vote have not been matched by May.

It was Cameron who memorably dubbed Ukip as a bunch of “fruitcakes and loonies and closet racists mostly”. This returned to haunt him as pressure from Ukip forced him to foolishly promise an EU referendum. But his quote is a reminder of the dangers of allowing the Ukip tail to wag the Tory dog. The new recruits will be more likely to elect a Europhobic, right-wing leader with a hard line on immigration, even though that issue has fallen down the list of the public’s concerns since the 2016 referendum.

A Trump-like Little Englander party and a nationalism that flirts with racism might cheer the Tory members who welcomed Boris Johnson’s inflammatory remarks about women who wear the burqa. But it would consign the Tories to the electoral wilderness.