Engine Management light / 02 Sensor fault

Hope someone here can help out with this problem, My uncle has a 2004 x-type 2.1L petrol v6, his engine management light has come on, so he took it to a local garage who said the o2 sensor was faulty so replaced it. The light came back on 20 minutes later, so they replaced it again, charged him £160 in total for both changes and it hasn't fixed the issue. 

I had him take the car to the garage of a friend of mine who has found that there is no voltage reading to sensor 1 bank 1, and a reading of -0.14v on sensor 1 bank 2. 

My uncle doesn't have the manual for the car to show which fuses are which, and when I've tried to search online for the correct diagrams, none of them match the fuse boxes he has in the car, so I'm a bit stumped as to which fuse or relay needs checking. I will attach pics at the end of this post. 

So what happens is when the engine is cold, if he tries to accelerate with any more than a touch of the throttle, the engine will stall. If he lets the engine idle up to temperature before driving, the car will stutter some times under acceleration, almost like the car doesn't spark for a revolution of the engine and then carries on as normal. This might happen once, or sometimes every few feet of driving. Also when this happens, there is a click from the relay under the nearside footwell. 

We are unsure now exactly what and where we should start checking to get this problem sorted, so any input is greatly appreciated. 

We are aware of the dodgy wiring mod, however this was done for the headlights by the previous owner. Not sure if it could be related to the problem, so if you have an idea about it please let me know!