Thanks for the suggestions everyone. It has been stood around six weeks yesterday (battery is fine though), so maybe its just a cheap combination of pads and seizing etc.
LPG conversion being done at Worsley Autogas, they are my nearest approved installer. Met the guy there today and he explained what it involves. £1920 all in for a BRC Multipoint system with a 92ltr doughnut tank in the wheel well.
Is there anything i should ask the mechanic to change on on the engine while he does the conversion, things that might need doing in future that would incur additional labour if done separately?