Indeed, Helinut is correct. Trustees have a rubbish job: it's not paid,yet they can go to jail if things go wrong. It sounds to me like the Articles of Association of the charity state 'for the county of Wiltshire' and until these are changed, that's all the funds can be used for.
I - for my sins - am a trustee of another Air Ambulance trust, who set out to raise funds in another county with a view to launching a second machine in this county once enough funds had been raised...in that county. We're very nearly there after just 12 months!