Moondog,
Thanks for the suggestion to get hold of a bilingual SALT - we had the appointment on Thursday - and she's going to be working with ds's school and us to sort out the problems.
It was good just to be told that I wasn't being a neurotic mother about ds's speech - he has a really huge vocabulary,and has a lot to say, but gets frustrated when people don't understand him. The problem has been more pronounced in Welsh, as the consonants he has problems with are really important in Welsh! Try speaking Welsh without c, g, th, v sounds (amongst others)
Anyway - thank you!
ejt
Best £90 I think I've ever spent!