Gay marriage was David Cameron’s ‘poll tax’. Like the poll tax, it passed through Parliament and was successfully implemented. Both measures had something to commend them. So far as gay marriage is concerned, Cameron was ‘very honoured to have been prime minister….enabling those who love each other to get married whatever their sexuality.’ Even those of us who have reservations about gay marriage can see that the point he was making.

There were arguments in favour of the poll tax too. Reform of domestic rates was a long-held Conservative intention. Who could deny that the little old lady living alone should pay less tax for local services than the smaller house with four earners next door? Reform of domestic rates was long overdue. When the poll tax was explained to Margaret Thatcher, such was the antipathy to rates that Minister William Waldgrave was able to say with a flourish, ‘you will have fulfilled your promise to abolish rates.’

And yet both gay marriage and poll tax shared a common flaw. Forgetting the the moral arguments behind both measures, what it comes to is a simple matter of political arithmetic. Both gay marriage and the poll tax upset more voters than they gained. For every little old lady who was grateful to receive a cut in her ‘unfair’ domestic rates, there were two or three more who were disgruntled by their increase. True, most of these were not Conservative voters. But enough were and the net effect of the poll tax was to lose votes for the Conservative party.

The same is true for gay marriage. So many who voted Leave opposed gay marriage. True, many of us had serous doubts about David Cameron from the beginning but it was the railroading of gay marriage under the ‘Conservative’ banner during the Coalition that finally and completely lost us from the Cameron camp. After the casual dismissal of deeply held concerns, David Cameron could never again count on the personal support of so many instinctive Conservatives. Like the poll tax before it, gay marriage lost Cameron more political support than it gained. When the big issue – the EU referendum – came along, there was no trust, no personal loyalty and no personal support for the Prime Minister. Had he handled gay marriage differently, likely he would have won the EU referendum and still been in office.

So what about grammar schools? Again let us ignore the arguments for or against selection at the age of 11 but look at the simple matter of political arithmetic. Suppose we have large grammar schools and they offer places for the top 20 per cent of the ability range. A fifth of children will ‘pass’ their 11-plus exams and get to these highly esteemed schools. On the other hand, four fifths – 80 per cent – of the ability range will fail. Now many of these children ‘failing’ will be children of parents who would never vote Conservative. But not all. For every Conservative voter who is happy that his child has ‘got into the grammar school’ there will be two or three who are unhappy that their children have ‘failed’. One does not need to have a long political memory to remember that the reason that Margaret Thatcher closed more grammar schools than any other education minister was that they were a political vote loser for the Conservatives. As Simon Jenkins recalls ‘The eleven-plus…lost them the 1964 election.

It may be that, at the moment, neither the Conservative Party nor Theresa May, needs the votes of all potential Conservative voters. But things change rapidly in politics. The reintroduction of grammar schools may make more enemies than friends. The latter, as we know, come and go. But the former just accumulate.