The turnout in the Conservatives’ Totnes open or postal primary of 2009 was almost 16,500.  Sarah Wollaston, its victor, went on to win the seat by roughly 5000 votes, gaining a 46 per cent vote share.

A year later, the turnout in the Gosport postal primary was just over 12,500.  Caroline Dinenage won the primary, and went on to chalk up a stonking general election majority of almost 14,500.

Needless to say, it would be foolish to claim that Dinenage’s bigger majority was caused by her smaller turnout (or indeed her smaller share of the primary vote – 39 per cent to Wollaston’s 48 per cent).

Or, indeed, to assert that because the turnout in the Rochester and Strood postal primary was about 5700, Kelly Tolhurst, the victor, will win the seat by about half Dinenage’s majority – some 7000 votes.

Certainly, the turnout figure that the Conservatives have announced this evening is extremely disappointing for Downing Street and CCHQ.

Both plainly hoped that the event would capture voters’ imagination.  Clearly, this hasn’t happened.  (Tolhurst beat Anna Firth by a sliver – 50.4 per cent to 49.5 per cent.)

Perhaps matters would have been different if the process that led to Tolhurst’s nomination as one of only two candidates had been more transparent, open and voter-engaging – and perhaps not.

None the less, a turnout of half Gosport’s cannot fairly in itself be described as a disaster.  Six thousand voters had a say in the Tory selection.  That’s about 5900 more people than had a say in Labour’s.

And UKIP’s Douglas Carswell, one of the pioneers of open primaries, will presumably be pleased be to see another postal primary in action.

(Carswell himself was not selected by his party to fight the Clacton by-election by a postal primary.  Nor has Mark Reckless been in Rochester and Strood.)

None the less, context is everything  Tolhurst needed a bigger turnout for CCHQ to re-gain the initiative after today’s ComRes poll showing UKIP forging ahead in the seat.  It didn’t happen.

But the alternative would have been for CCHQ to hold an open caucus meeting – and there would have been no prospect whatsoever of some five and a half thousand people turning up to one.

And the involvement of so many people in the selection will help CCHQ to build a campaigning base for next May’s re-match – if Reckless wins in a few weeks, which he certainly will on present polls.

I’m not an enthusiast for a CCHQ-imposed system of postal primaries, and think that the shortlist put to voters in this one was, well, rather short.

But as Mark Wallace has said on this site, holding one in Rochester and Strood was the best option for the party to take – and one that should have been taken in Clacton.

Tolhurst said in the wake of the result that her priorities include “action, not just talk, on immigration, getting Medway Hospital out of special measures and fighting to stop the development at Lodge Hill”.