Alan – very many thanks. Really appreciate it. OK – update: recovery guys (home start cover included with insurance) traced the fault to “no power to the trickle wire and thus no power to the starter motor”. We hotwired it – and – hey presto – all starts fine. So we started the engine a couple of times and then tried it again with the key: nothing.
The car is a 1995 AJ16 4l 6 Celebration. Apologies now if this is an idiot question, but is there a relay or fuse that could be responsible for the trickle wire and starter motor not receiving power? Sorry if this is a dumb question.