Thank you everyone for your quick responses. It's nice to know it's not just me and my driving!
The problem is when it is is Drive - and a 1 in 5 hill is not too excessive (not on the Isle of Man anyway). I also had an automatic before which was no problem at all - in fact it was a boon, as the halt sign in question is particularly awkward on a busyT junction - with poor visibility aswell. In my other automatic you just drove up to the stop sign, held it on the foot brake and then just took off and hey presto you were away - no need at all to use the handbrake. Looks like I will have to get out there and practice or think again whether I want to keep the Lexus. I would feel very hard of parting with it though.
PS Even 'him indoors' finds it tricky!!!