Thanks all
My moving average was 18.8mph, but I was stopped for just short of 30 mins to give a total average of 18.2mph.
It just goes to show how quickly you can improve. 3 months ago I'd not ridden a bike this year. My first ride was a 50 mile hilly ride with an average of 15mph and that really hurt.
Anyhow, here's my training plan if anyone's interested (note how it's all outside of working hours):
Tue - 10 mile TT inc. riding there and back (20 miles each way)
Thu - as above
Sat - Ride at 75% maxHR of increasing distance
Sun - 3x hill climbs up a 1 mile hill