So you used to get it, but now you don't?
Have you re-scanned/re-installed the TV since the switchover? Remember it was done in 2 stages over a week or so, so you'll have need to retune after the latter.
Do you live in Swindon or elsewhere. If you are on a 'border' of two digital areas you may need to manually tune. Alternatively you may just not be able to get it any more! There are several more stages to go and you may need to wait until next switchover for it to be restored.
I guess you don't want to put your post code up here, but check the digital TV website to see what channels you should receive:
http://www.digitaluk.co.uk/If you put in your post code and house number, then pick which transmitter you are tuned in to, then you can dig down and see which channels you should be able to get at each stage of the changeovers.