harley, some manufactures tell you to disconnect the battery and touch the terminals together this discharges the static (quicker than pulling fuse and waiting 24 hours)
Lechat was the car smokey? some cars suffer from the inlet manifold/throttle body getting chocked up with crap and needs to be stripped and cleaned
and and how on earth was a cam sensor + diagnostic+ fitting +vat =280 quid? this seams steep
explain to them nicely that you asked them to diagnose the problem,and that you have payed them 280 to fix it and it is still the same/ worse,ask if they quality controlled the work of the mechanic as you cant see any improvment with your vehicle for your financial outlay
Ask if they can check the current data with the engine running, this will give you specific values ie fuel pressure as this is critical , fiats wont start with less than 170 bar pressure at cranking speed, also a sticking fuel pressure regulator should show up