Guys thanks for coming back to me so quick with your suggestions. I had wondered about that restricted route entry in the log and couldn’t find a single mention of it anywhere FreePBX.
In the mean time I decided to check everything that both of ye suggested. In my outbound route under Extension routing I found that for some reason my extension (501) was in the blocked field, this is dispite the fact that I have made doubly sure before I wrote this post that I had it in the allowed field. Again as I said at the start, I’m totally green to Asterisk and FreePBX so I clearly did something stupid. Anyway, I have now moved my extension into the Allowed list and I have configured my Codecs in my Soft SIP Client to match the order of the Codecs offered in FreePBX Advanced Sip Settings. It’s now working exactly as I would have expected. So thank you again guys for all your help and for taking time out of your day to assist me.
On a side note, @Dave Burgess my networking at home is (in a word) overkill. I have 14 subnets performing all sorts of roles. All running in a Layer3 configuration with ACL’s all over the shop. I’m totally green to Asterisk and FreePBX but not to networking, I’m a CCNP certified engineer so I can stand over my network 
Again thanks very much guys. You’ve made an Irish man happy tonight.
Beers on me