Hi all, thanks for the feedback.

Peter J - The garage is very dry and well ventilated so no moisture however it is not heated so I guess a bit of condensation could build up. It's odd then on that basis that it was fine from cold and only caused an issue 10-15 mins in to the run.

Robbie & Alistair - That's a good point, I'll double check the battery earth particularly as I do occasionally get a "Tick, tick" on first press of the starter and then ignition off an on and the second time is perfect.

Cheers, Paul