Seems that this thread has grown wings "pun intended" the beauty of PPRUNE.
I appreciate all the comments but the only reason I asked was to find out if it was a common practise I had never came across it before and as most people here seem to agree it is more of a goodwill thing than anything else.
I suppose considering the cost of helicopter flying it stands to reason the school would need some recompense if it had a few regular no shows.
I suppose it was the fact that I was asked to sign something that rankled me slightly but then that is modern society I suppose.

Providing the percentage is not excessive and reflects the amortised costs of the use of the aircraft/instructor then it is unlikely that such a clause would be held to be unreasonable. The key here is the lack of notice regarding the cancellation as it prevents the flying school trying to re-offer the aircraft (for example to a student who is available at short notice).

The unfair contract terms legislation deals with clauses that attempt to remove or limit a consumers ordinary rights (for example excluding liability for negligence etc). Here the term of the contract simply requires you to give some notice if you decide not to honour your booking. It's not dissimilar to hotels or restaurants asking for a deposit/credit card number with a room booking/reservation and requiring any cancellation to be made by a certain time.

Me dentist and me optician both charges us if i don't show! Why should me flying school be different?