Visibility is the only long term answer,and it is a deterrent in
itself, but apprehension of the violators is necessary so that the use
of the means of visibiility is seen to be exercised.

Mind you, if you have ever ridden the Tijuana trolley from San Diego
to the Mexcican border, the grippers have :-

1 A Nightstick
2 A pistol
3 Pepper Spray
4 A ticket Machine and cash bag

There is no vandalism and everyone pays up! Seems the Scwarzzenegger
method works; so how about taking some of those people off the
platforms of Piccadilly station and actually placing them on train to
both assist the present crew and provide some back up along ther
journey