well just to give you an update, popped back to main dealer today, they had another diesel filler neck in stock, had look at it, it was different from the one that is currently fitted. i asked the chap to bring up the filler necl for the petrol engine, guess what, that one matched the one which is currently fitted. so now i know what the problem is, i will be looking in scrap yards near me to locate a diesel fiesta & remove the filler neck & then fit it to mine. and then hopefully stop this leak once & for all.