Fox hunting is illegal, it was banned by the Hunting Act 2004 in England and Wales and the Protection of Wild Mammals (Scotland) Act 2002.
There are exemptions in the Hunting Act to allow certain types of pest control, please see the link in 'related information' for details.
Hunts in England and Wales invented the activity of trail hunting after the hunting ban came into force. This is a non-lethal sport where the hunt follows a pre-laid trail rather than chasing a fox.
If you believe a hunt is using trail hunting as a cover for illegal hunting, this can be reported to your local police force. Some police forces also have an online wildlife crime reporting form.
If an illegal hunt happens on public land, you may wish to raise a formal complaint. Hunts may only use Forestry Commission or MOD land under a strict licence. Breaching that licence can mean the hunt are no longer allowed to use that land. Similarly, charitable bodies such as the National Trust, Woodland Trust or local charitable trusts or parish councils will take a dim view of law breaking on their land and may remove any 'sporting rights' they have given the hunt.