I've tried to explain that there is no need for any specific law concerning use of cellphones in aircraft as a de facto one already exists.
All emitting devices used in aeroplanes must be licensed. There is an exmption to this requirement that allows the use of 1800 MHz GSM cellphones in aircraft fitted with pico-cell terminals. Hence no other use of cellphones is lawful in aircraft registered in the UK or flying in UK airspace.
It's quite simple - but perhaps not sufficiently so for some, it would seem.