After some more investigating, I have discovered that the fuel return pipe into the tank seems to have been crushed.
Would it sound logical that this could be causing the drastic drop in pressure, hence the 'fuel leak'? I have replaced the fuel lines too the injectors which were previously saturated, once again, same issue. I would assume this could be connected to the crushed line..
My thoughts are that at speed and high revs, the fuel is being returned at a higher rate than Idle, and as such cuts out then when at traffic lights
Any thoughts would be appreciated!