It is true that there is a substantial UK GA sub-community which never checks notams (in most cases because they do not have internet skills) and I am sure they rarely check the weather too (unless BBC TV counts as a preflight briefing).
There is probably no short term solution to this. The problem is not helped by the 2-yearly flight with an instructor not (normally) being used to check preflight activities.
As regards reliance on GPS, I do wish some people got off their pedestals and accepted that WW1 ended in 1918 and WW2 ended in 1945, and times have moved on. Most people who go places seriously do fully use GPS and are not interested in jacking up their cockpit workload by timing each leg and identifying villages, lakes, railways, etc. The year is now 2011 and the establishment old-timers (members of the Royal Institute of Navigation, no doubt) need to realise that there are pilots who are flying modern planes, who go to real places not just around the corner, and if dead reckoning was the only way there would either be little or no long distance GA activity, or there would be mayhem. The really old timers in ATC did have to get a PPL originally but most of them rarely used it. There is also a large community in GA which never goes anywhere (probably the same people who never get notams) so they don't need advanced navigation, and can't see why anybody else should need it.
One normally backs up GPS with VOR/DME but at UK GA (sub Class A) altitudes there is often no navaid reception. And higher altitude flight around the UK (where navaid reception would be fine) is frustrated by the virtual inability to get an enroute clearance into Class A - another artefact of the tightly compartmented UK "airspace management system" which consigns VFR traffic (actually, more correctly, all traffic not on Eurocontrol IFR flight plans) into a low level dustbin.
BTW, every GPS is easily capable of BRNAV and PRNAV lateral accuracy. Getting the PRNAV approval is a whole another story.