I thought I'd give you all a further update. I had my appointment with the surgeon on the 4th August, and had booked an appointment with another AME for the Monday after (8th August).
The surgeon was happy to discharge me, and agreed to send me a letter following the CAA format that I could take to the AME. On the Monday morning I hadn't received the letter so I rang the surgeon's secretary. She explained it was ready, but she hadn't sent it because she didn't have my email address. I gave her the details, and within a few minutes I'd received the letter.
I then forwarded that on to the AME (as per his request) so that he could have a look before my appointment. The appointment went off without a hitch, and the AME signed me off.
There was, however, one minor spanner in the works. The surgeon said I could fly from the 18th onwards, which ruled out the week I had booked off work to fly (10th, 11th and 12th) and the AME wouldn't overrule him as his experience is obviously greater.
As annoying as that was, it has also to be said that however good my ankle felt, it certainly wasn't 100% so it was probably sensible not to fly anyway. If the AME would have signed me off there and then rather than saying wait until the 18th I would probably have questioned my own fitness to fly anyway...