To conclude. Just rebuilt the circuit on a new Pcb and it all works great. I realised that the Previous PCB was near a radiator, didn't realise the heating in our building had been turned on so maybe the board had twisted or something. Anyhow, really grateful for all help given and shared knowledge. Been really good for helping me to learn how to diagnose faults and I now have a reliable power source, FINALLY. Thanks folks.