I noticed fuel pump wasn't priming, linked 12v across relay swich and pump started to prime so I suspect and have ordered another relay.
Sounds a good possibility , I will give theoil try andIs piston 1 at tdc though. I'd throw no more parts at this until you found what the issue is with compression. I had a astra a few months back with same issue and low compression like your and it had been cranked that long it had washed the bored down. Had to pour a load of oil down each cylinder and turn it by hand with the plugs out. Then suck as much oil as I could before refitting the plugs. Make sure plugs are bone dry. Heat the tips over a flame to dry them. One refitted it went first go. It was unreal. Never seen borewash drop compression to less than 5 bar. The cars still running fine today and compression was later checked and all had returned to over 13 bar.