Hello,
The best thing would be to pop it into Alltec or any other company that deal with machine repairs.
If there is no one local, the lads in the workshop suggested using a tool that will gently grip the regulator and try turning anti-clockwise using a maintenance spray (like WD40) to grease it as you try to turn it. Don't take the regulator off completely or all the components will drop out.
If you would like to speak with one of the guys in the workshop, call us on 01763 208222.
Karra