I have already posted two CAA pages which confirm that it is illegal.
Those airline passenger advisory website pages are not
law applicable to
private flights.
For GA, you need to find a reference in the
ANO. The PDF is called CAP393.PDF and you can find it at caa.co.uk. When you have found the reference, please post it so we can be suitably educated.
In a nutshell, the way the law for GA works is this
Civil Aviation Act
Air Navigation Order
and then you have
LASORS (odds and ends delegated to the CAA to fix as they wish)
Everything else is basically
advisory, not
law, or is simply bull!!!!!