Well, we were all signalling the overproduction of TBs for racing two, three years back, weren't we? Foals were being given away during the last three years, or simply left at auction horses, unsold. Those were the 'good' ones. The rough pony, the half-draught, the trotting pony and any amount of rough wee souls with hairy chins, let loose in fields and allowed to breed indiscriminately without proper - or probably any - veterinary attention, decent food, let alone training and human contact - well, they're destined for the rubbish heap.
Best thing now is to shoot what can be shot ('cull' is a pretty word for mass slaughter), repair what's worth repairing, and then get the changes made FAST to legislation so that 'the disease' of horse ownership without responsibility or ability becomes a thing of the past.
It's a very sad and dreadful thing to contemplate, but it's not as bad as thinking how thousands of innocent horses and ponies will end their already miserable lives. Get the shooting done with asap (old/sick/injured/crippled), get the repairs made asap to the younger, well-made and potentially reusable, make all ownership a matter of national registration with microchipping for all, and ensure that the welfare charities have the teeth to go and seize what needs seizing in future. First case of neglect, cruelty, inability to fund or cope - seize, confiscate, ban ownership for life. Keep a national database updated so that the banned can't squirm into ownership again.