I'm actually back up to scratch again here. Speed tests are fine, pages loading OK.
Files at
http://fuller.zen.co.uk/test/ coming down at the correct speed.
That said, I have changed my IP address twice tonight and rebooted all kit about a dozen times.
Finally got everything working again.
I know I'll have spoken too soon!
Makes me wonder how the poor folk who haven't a clue how to resolve things go on.
Especially when Bombay tell you a crock of smelly stuff.