Hyundai Tucson 2005 CRTD CDX - Engine misfiring - lardy

I was driving in France recently and having refuelled I drove about 200 miles on the autoroute at about 80mph. on decellerating to enter services, the engine started to misfire and run rough. I stopped it and restarted with the same result and was evenyually towed off to a garage. The French garage tried changing the injectors with no improvement and stated that they had checked the fuel line (first thought was dodgy fuel), still the same. It's now back in the UK and my garage are trying to find the fault, the injectors are ok the fuel line clean, high pressure pump very slightly low on pressure but not by much. When started from cold it runs evenly but when it warms up it runs rough with no.1 cylinder not firing, which is furthest from the H/P pump. Interestingly, the deisel they removed smells of paint thinners, any ideas?