Well, I would say that under new labour public services got less quickly screwed than under the previous conservative governments (although we've still not seen the full ramifications of PFI). The following conservative government had a very rare opportunity to run with that, labour in 2010 and 2015 ran on austerity platforms that would have screwed public services a bit more slowly than the tories did though. If you keep electing labour governments formed from the right of the party then how does that protect public services? They get run down a bit more slowly? Isn't that abandoning ordinary people? If you want to protect public services then you need to be supporting a party formed from the left of the labour party. The more you argue for a party from the right, which does not support social democracy, the more you solidify the idea that social democracy is radical, unthinkable. It becomes less likely to happen. Public services will die, back to the victorian age. Maybe you can delay it by a few years but you can't stop it let alone reverse it. I want a path to social democracy, not away from it.
You don't get change by voting for it. You get change by forcing capital to yield more of the outcomes of capitalism to the working class. The voting part of things happens almost as a byproduct of that. If you put enough pressure on capital then the only realistic choices available to vote for will be ones offering a better settlement, if you don't then your choice will be shit or shitter. Somewhere in between that lies ok and shit and I guess the possibility of better and shit but that's rare I think. Ultimately that pressure expresses itself through the state which means voting, but the change comes before the voting, not as a result of it.