Hi ex matelot. Thank you for your suggestion. The computer has Windows firewall, Avast free version and Spybot, all up to date and running live with, additionally, frequent on demand running of Malwarebytes and CrapCleaner. What is that HouseCall brings to the party, please, which isn't already covered?
cdtaylor nats and mixture, I don't understand this "swap" issue because I've never heard of it but could this explain hard drive usage swings of 30Gb - especially on such a small capacity machine? Did you suggest it in response to Madame often having 30+ tabs open in Chrome?