Would you believe it?
I've had this problem for 2 weeks and I solve it minutes after writing that post.
A mate of mine found a thread on the Steam forums whereby you enter this command in the launch options...
+voice_forcemicrecord 0
Now working absolutely fine!!
The thread is here...
https://support.steampowered.com/kb_...hp?p_faqid=237
Sorry for wasting your time but I hope this solves other peoples problems should they encounter a similar predicament
