Just a quick update on this. Car is now running like a dream. No headlight issues, no crazy flashing dash lights or flat batteries.
I found a few issues contributing to the problems, such as duff HIDs, puddle of water under drivers seat with electrical connectors lying in, very badly installed alarm, with bare wires all over the place, but the main issue was, the power cable from the battery to the fusebox was only attached to the fusebox with 1 thread of the nut so the battery wasn't charging correctly, in fact not at all.
Car is all sorted with 1 big happy joe