I think Growmore is only active above a particular temperature anyway, but a general sprinkle around everything will be there for them when they start to grow. My Clematis have fat buds on too, but remember with Clematis...if it flowers before June, don't prune.

Don't apply Growmore or any other feed this month - March is the earliest for applying them, April in the north. Vitax Q4 us another option, but Growmore is fine.
As Volunteer suggests, you need to know which variety your clematis is before deciding to prune - if its one of the jackmanii/viticella group, these should be pruned back to 2 buds from the base right now.

I never quite know when to prune Clems as they are so many different ones arent they ? I prune in Sept and Feb; I think the only difference is ( I could be wrong) is you might lose a few blooms ! but if its untidy I prune! the first year down to 12" the year after that 18" and then just tidy. I think your just wasting any feed at the moment and as Bamboo says Im in the North East so dont feed anything until around Easter time.

Thanks folks for the info. So, is it OK to prune when frost is forecast?

Absolutely, Bernard - I did some last year with snow on the ground and air so cold it hurt to breathe. The viticella/jackmanii ones must be done by mid February at the latest, regardless of the weather.
Maggy, as long as you know the varieties of clematis you have, pruning's not difficult, and some don't need pruning at all.