I finally have some better news to report. Having no luck with identifying any external causes I revisited my LW settings. It occurred to me that the issues I have been having with crashes and hanging seemed to coincide with issues I was having with internet speeds while running LW. Specifically when I was running LW I couldn't seem to do much browsing - it would take ages to load some ages and some would not load at all.

I then checked the Download Bandwidth setting in LW. It was set at 100%. From memory I think I set it to that because I thought it would help download speeds. I reduced it to a speed of around 25 KB/s which is roughly the max speed I get on a 256K ADSL connection. Since doing this I've been leaving LW running for long periods day and night and haven't had any crashes. Internet browsing is also much better.

It's certainly an improvement so I'll see how it goes