In reply to all.
Thanks for the replies and personal emails - much appreciated. Here's an update.
Why oh effin why didn't I follow my instincts on Monday!!
We went to the vet this morning. Apparently I was bang on with my own diagnosis - lacerated flexor tendon which the first vet completely missed. The cat will need an op but apparently it might be too late to re attach the tendon but he's going to try and at least sew up the wound.
On the + side he's quoted us only 110€ + the cost of antibiotics which is better than we expected.
Thanks again,
E