Vauxhall Zafira first start

Ongoing problem:- First turn of the key to start (cold engine) just won't start second turn and the car starts, this happens consistently.
From the history that came with the car this has been an ongoing issue for a long time.
Attempted repair by first garage a non return valve was fitted into the fuel line.(no use) Second garage replaces the glow plugs (no use) Third garage say they fixed the problem cam sensor renewed and pickup cleaned. New water pump idlers and adjuster.New timing belt and anti freeze.(no use). Now I am being told it might be a wiring fault and there will be extra costs until they just happen to find the fault.
I saw online that the fault could be a water temperature sensor this was checked and no fault. Has anyone had this problem? Yours truly desperate and penniless.