Since you're having a 'tidy - up weekend' sure go ahead and clean up your hydrangea. It's really up to you when you do it, or if at all. Either way won't hurt the bush. I do mine about now too, just as it starts to wake up.

The old flowerheads protect the new growth from frosts, so I wouldn't do it till the danger of frost has passed, ie. next month (May).

I've done mine this week and the second set of buds will also flower if the top ones get affected by frost.

I did mine a couple of days ago. Its normally better to do it in Spring than in Autumn. The probably reason why yours didn't flower before was that you pruned too heavily. Try just taking off the old flower stem rather than cutting it back a long way.

Thanks everyone, I will do tomorrow as I have tidied today and noticed lots of lovely spring growth everywhere and they do look a bit unsightly!