If you want it to have a showroom finish you will want a decent detailer. Although some consider it to be the same thing, usually performed by the same people, valeting is generally seen as a standard service, while detailing is 'the whole nine yards' service.
Valeting takes 1 or 2 hours, but detailing can take 2 days.
As with anything the better service will cost you more.
If you google wirral detailer a few results come up.
Also have a look on www.detailingworld.co.uk
, they have laods of members that can provide the service, so should have a few local.
I would suggest when enquiring, asking for some examples of previous details, before and after with progress shots if they have them too.
Many of them like to do progress diaries on the jobs they do (check the Showroom area). Check out some of the details done by Baker21, a detailer that has done some prestige cars as well as the usual runabouts. Link to Baker21 Showroom Threads
He goes really in-depth and shows how much work they put into detailing, as opposed to a wash, wax and vacuum.
Hope that helps.