OK, I've got a big race a week on Sunday (12th March) so I 'm planning to taper next week. I'm tempted to train hard this week though as I feel good and think I could recover sufficiently with a 'easy' week to follow. Is this a good idea?

Really depends on the amount of training you are doing and the length of the race.
For an XC or 10k race for example I would only miss a hard session on say the Thursday and replace with an easy run. So for example I do circa 60 a week with a couple of rep sessions and a long run (usual basis) I would run steady on Wednesday, say an 8 miler, 5 or 6 on the Thursday and for a Saturday race an easy 4-5 Friday or a day off.

Depends how long your big race is...

I'm targetting the MK Half Marathon as quite a serious race this year (also on the 12th March) - and for that I'll taper by:
- running normally this week (14.5 miles on Sunday)
- running a shorter speed session than normal next Tuesday
- running only short steady 5km runs next Thursday
- not running on Friday or Saturday

Of course, I'll also do some swimming and eat way (weigh?) too much...