Posted this below on someone’s reply but just incase you miss it.

Legally you have to have permission of the landowner to even step foot on his land with your machine otherwise it counts as trespass with intent to commit robbery and you can literally get jail time and police can seize your detector and your finds collection. Usually as part of gaining the permission you would sign an agreement with the landowner to say “we split finds over the value of £50 50/50 or 70/30” or whatever you agree on. That way if the police stop you you can produce the agreement to show you’re allowed to be there and you’re protected against any funny business if you find something good and the landowner tries to claim it’s his.

Legally you have to have permission of the landowner to even step foot on his land with your machine otherwise it counts as trespass with intent to commit robbery and you can literally get jail time and police can seize your detector and your finds collection. Usually as part of gaining the permission you would sign an agreement with the landowner to say “we split finds over the value of £50 50/50 or 70/30” or whatever you agree on. That way if the police stop you you can produce the agreement to show you’re allowed to be there and you’re protected against any funny business if you find something good and the landowner tries to claim it’s his.

Unfortunately he will have to declare it as a “treasure” (it technically belongs to the king) so he won’t get anywhere near the value for it. Most I’ve ever found detecting is a load of tent pegs and a few coins on the beach so I’m not 100% on the process but I’m pretty sure it gets auctioned to the highest bidding museum and then he will get around 10% of whatever it fetches (minus any agreement with the land owner of the field he was searching in). Rest goes to the crown. Still a great little find though and will no doubt pay for his next detector.