In reply to Ella Morris:
Lots and lots of DofE work available, especially at weekends, through March-July and September-October but usually means walking around, e.g., Surrey or Oxfordshire rather than real mountain work. Generally £130-170/day depending on provider & whether nighttime work included. Long but fairly easy days teaching young people.
Less predictably there is work on 'real' mountain stuff - 3 peaks, Yorkshire 3 peaks, charity ascents etc - but not easy to find regular work unless you are doing it full time.