Well that wasn't as bad as expected. Tavistock Tyres tested the wheel, couldn't find a leak, so resealed the tyre at a grand cost of £9.95. The invoice said 'puncture repair' which makes me think of those little rubbery patches you get for inflatable airbeds, but I have checked the tyre and I can't see any little green squares stuck on the outside ;-p so I assume they know what they are doing!
So far, the tyre is still inflated. Fingers crossed it stays that way.
Mollydog is pleased that her normal chauffeur service has resumed.