Kevin at Wickford is first class. Old school mechanic. No salubrious surroundings (who cares, the quality is in the workmanship). Does it right first time with quality parts. Used him many times. He'll probably be able to diagnose without the use of T4 using experience gained over many years.
I think he may be on holiday for a week at the moment.
You could try the guys at British legends in Sarfend (they have T4 should it come to it) if you need it looked at quicker.
http://www.britishlegends.co.uk/ Not used them myself, though as Kevin is closer to me.