Mike,

AV - Nothing wrong with installing just the AV component of the CA suite

I removed each of the four components in turn but even the AV component
alone made things very slow.

How is the PC connecting to the net?

ISP supplied modem/wireless router. I'll investigate your various firewall
suggestions.

.. it is essential that at the very least you install the 290700 patch for system restore

That was the first thing I did. Prior to reinstalling, I tried using system
restore only to find no restore points and the date shown as 31 December 1899.

regards,
Calum