Is the door locked shut? If not it shouldn't be too difictult
Took a lock smith about 5 minutes when someone broke into my mums house and stole her door key
Would think homebase would sell them, just get one as close to the original as possible as the replacement she got is pretty good but not quite as flush fitting on the inside.
I guess something like this indicated they do:
http://www.homebase.co.uk/webapp/wcs/stores/servlet/ProductDisplay?langId=110&storeId=10151&partNumber=001809