...nothing at all, and the clue is in the turnout of 34%.
The proper place to discuss civil liberties was at the general election, when both parties put their different visions in their manifestos and everyone got to vote, and what's more the turnout would have been high too.
Instead Davis declared that fighting his own safe seat (after persuading his main opponents, the Lib Dems not to stand) was a referendum and that everyone would be enthused enough to debate. Well they weren't enthused.
Some will say, never mind, by-elections don't normally have high turnouts. Well, there is a very good reason by elections don't have large turnouts - and that's because the by-elections don't decide anything of importance. Only in hung parliaments do by-elections have a significant effect on who runs the country, and hence on legislation. By producing such a low turnout, the voters in H&H were saying "nothing important here to decide, I'll stay indoors". And that's the most damning judgement of all.
Actually no, I'm being unkind to David Davis. He's achieved one thing - he's ensured that the shadow cabinet member who took the most Labour scalps is exiled to the backbenches, and his replacement is a wet noodle who won't trouble us. For that, the Labour party thanks him.