Thank you TMR.
Over a pint last night he was able to look in the other place and inform me of a nasty Microsoft Update which disables Zonelarm and blocks access to the interweb.
I knew that my problem was probably caused by this, as everything went pear shaped after a re-boot.
Update now removed and everything is now ticketyboo.
Will email MS with a bill for time wasted - won't hold my breath though.