The UK abstained. Why couldn't we just abstain?

There's no reason to hide a righteous point of view. If you have a valid opinion you should express it and a veto does just that. In the words of our ambador - This resolution does not display an even-handed characterisation of the recent events in Gaza, nor does it advance the cause of Israeli-Palestinian peace to which we aspire and for which we are working iduously," he said