Hi Richard,
I understand, and it's a difficult one because I wouldn't want to dampen down the spirits of any local enthusiastic groups. That said, it can be exceedingly hard to get serious numbers for NHS Hack Days (even the London NHSHDs get a maximum of around 150 attendees - and it's much less outside of London). Without enough attendees it's hard to get the same kind of atmosphere and the correct balance of skills to be able to have something to show for a weekend's work.
With this in mind I'd be cautious of running too many NHSHDs per year because people only have a certain amount of available time for such pro-bono weekend adventures, and so having a Surry NHSHD might adversely affect attendance at the other ones.
I think I'd tend to advise that, at least initially, those enthusiastic individuals from Surrey might come along to the Gloucester NHSHD in October, or the next London NHSHD, both of which are within a 2 hr (ish) travelling window from Guildford.
That said, although we are starting to take a more professional approach to organising and running NHS Hack Days, with a more formal core team and governance around sponsorship etc, we are unlikely to stand in the way of local independent grassroots events.
Marcus