Oh good grief! Another flying club lawyer sniping from the armchair.
........Not zero, but near zero and if he and the other 'idiot', as you term them, are happy to accept the trivial risk for some harmless fun then good luck to them
Delta V. I'm most certainly not a lawyer. In this part of the world it is most certainly not looked upon as "harmless fun"
The rules here for VFR flight are below 1000'AGL or 3000 AMSL" which ever is the higher of the two you must be clear of cloud and in sight of land or water, above these altitudes you must the 1000' vertically and 1nm horizontally clear of cloud, other wise you need to be flying IFR on an IFR plan.
Obviously the UK has a far more relaxed interpretation of VFR flight.
If it's legal in the UK and while it's no doubt fun, I'm not convinced it's smart.