My personal opinion is that snow chains are tad overkill for the OP, seeing as he's talking about the M23. I guess a set of Snow Socks (available from Halfords) might be handy on the off chance his daughter ventures up Box Hill.There has been mention of snow chains. Most of you know they are heavy and when needing to be used, very cold and heavy! They will also be tangled into a right bunch of bastards, no matter how carefully they were stowed away!
Despite living in sunny southern Spain, I'm less than an hour away from a ski resort (yes, really!). If driving up the road to it after snow has fallen, the Guardia Civil can and do stop vehicles to see if they are carrying (mandatory at or above the snow line) snow chains. If not, they are turned back.
Now to the point - there is an alternative. They are fabric wheel cover things, dead light and take about 20 seconds to put on. Mine are called 'Easy Sock' or 'Snow Sock' or something. They take up the space of a rolled up towel and will stay in the boot in the spare-wheel well forever - or until The Guardia ask to see them!