I mailed them this afternoon and they responded impressively quickly. We were just exchanging diagnostic information when I solved the problem :
Basically I noticed that the version of wpa_supplicant on the linuxant download page was 0.2.3, checking around I realized that the latest release was 0.2.6 so installed this. This made no difference at all - exactly the same thing kept happening.
So going one further (not much to lose
) I then downloaded and installed the latest development release (v 0.3.4) - and this solved the problem. Everything is connecting fine now.
Connection speeds seem a little low compared to another dell laptop nearby so I'll continue to monitor that.
So now to check everything stays stable - but at least I have a connection!