Clive - my local battery distributor (a privately owned large auto electrical components factor) is happy to fill, charge and monitor at a sensible price (we've been customers for a lot of years). So there must be a few others out there.
Alternatively, a 'fill-your-own' pack is available from Lincon, who manufacture rubber cased batteries:
http://www.lincon.co.uk/accessories.html
While I have your attention - do you have any thoughts about my mention of them advising waste of time filling batteries with white on the plates on Champ's other battery thread?