Imagine for a moment that Alan Sugar renounced his title and joined the Conservatives, travelling to them via UKIP after an intensified period of Labour activism.  Now go further and picture him being elected to the Commons, where he stands to be Tory leader – supporting protection, championing veterans, bashing the influence of big money in British politics, proposing to stop Muslims entering the country altogether, and denouncing immigrants as venomous snakes.  There are claims that Sir Alan incites riots.  Conservative membership soars – with people joining the party who haven’t been engaged in politics for a long time, if at all.  Polls show that his candidacy divides Britain deeply, with more voters against him than for him.  Other Tory leadership candidates first dance to his tune and try to block him altogether, backed by a bewildered Party establishment.

We apologise to Sir Alan for this tall tale.  But it probably as good a British parallel as can be conjured to the story of his fellow Apprentice host, Donald Trump – who has been a Democrat and a Reform Party supporter as well as, now, a Republican.  Before dismissing it as impossible one should ponder the current fate not of the Conservatives but of Labour.  An extremist candidate did stand for that party’s leadership – Jeremy Corbyn.  Lots of new members did join it.  And Corbyn did win.  Britain is not as resistant to Trump-style sicknesses as we might imagine.

That said, it is much better protected, particularly as far as the Tories are concerned.  Corbyn was nominated because Labour MPs who should have known better (Frank Field, that means you!) put his name forward to party members as a candidate.  The Conservative Parliamentary Party does not give potential leadership candidates a similar free pass.  They have to battle it out in a secret ballot until the list of contenders is reduced to two.  Our imaginary Sir Alan would be very unlikely to make it through.

But even if he did, he would not go before a party membership recently swollen by an influx of cut-price members.  (A little-noticed feature of the Feldman Review proposals is that plans for signing up cut-price or even free members with full voting rights in leadership elections form no part of them.)  And even if he were first successful among Tory MPs, battling his way through to the final two, and then won among Party members as a whole, he would still be vulnerable to the no-confidence procedures that played such a part in the fall of Iain Duncan Smith in 2003.

Indeed, Corbyn himself is not invulnerable to Labour’s equivalent.  On this site yesterday, Mark Wallace set out the mazy tale of how the man who is now running the Opposition, if that is quite the right term, as a branch of the Stop The War movement could be defenestrated as early as this summer.  Labour MPs got rid of Tony Blair in a series of tortuous machinations – just as their Conservative equivalents winkled out Duncan Smith, and evicted Edward Heath back in 1975.

All this is a reminder that the British political system and the American one are not the same, and that an American Presidential candidate (if that is what Trump becomes) is not a British party political leader.  And once a President is installed it is beyond the power of his party to remove him from office.  In America, tea party politics takes place within mainstream parties: here, usually, it happens outside them.  Our Trump-type demogage would be more likely to do a British Donald by setting up his own party.  It is true that the British Parliamentary system, with its first past the post electoral system for the Commons, is insulated against new forces, as the current condition of UKIP reminds us.  But there is no law of politics that says it is immune.  And a paradox of the Conservative Party is that it is protected against Trumpism not by its strength but by its weakness – that’s to say, by the long-term decline in its membership.

Parties without strong roots in the communities they seek to serve will shrivel up sooner or later.  Our Party is not yet a Potemkin one – a front without a real house behind it.  But it is in danger of becoming so.  That the Feldman proposals are all take and no give suggests that they will do nothing to turn membership round.  What is needed is a balance that gives party members a greater stake in the party that, after all, is their property – some elected board members, more affordable conferences, a bigger say in policy – without simultaneously opening Tory doors to a flood of Tea Party politics.  This ought not to be mission impossible.  To claim that it is envisages a Conservative future of MPs without active members, representing seats in which they have no lasting hold.  If you want to know what is likely to happen next, glance back at the fate of Labour in Scotland last May.