My knowledge on this isn't up-to-date, so I'm sure there are others on here better qualified to give advice but, as far as I recall:
The kitchen doesn't have to be certified, as such, but all of the food hygiene legislation rules apply, whatever the size/turnover/commercial model or your kitchen.... and I presume you could be inspected at any time.
So you have to have all the separate hand-washing facilities and everything else that the legislation requires (within the prcaticalities of your set-up), plus have some degree of HACCP documentation in place.
Edited: 10/07/2012 at 12:51