With a large piece of the Thames recently gone dry, is it legal in England to detect the dry river bed?
There's some duff information being given above.
The simple answer is “yes”, but only if you have an appropriate permit; only on certain stretches of the river; and you are searching for personal enjoyment, not financial gain.
All foreshore in the UK has an owner, and you need the landowner’s permission to search it. There is no “public right” (although in some beach areas, the Crown Estate gives blanket permission). The PLA (Port of London Authority) and the Crown Estate are the largest land owners of Thames foreshore and jointly issue a permit, administered by the PLA. The foreshore is still defined as such, even when the river level temporarily drops to the extent it’s bone-dry.
The standard PLA permit is valid only for particular locations West of the “Thames Barrier” (a huge retractable defence system that protects the city from storm surges and exceptionally high tides) through to Richmond Lock, upstream. There are additional restrictions, such as around the Palace of Westminster and the Tower of London. You need the permit whether or not you are using a metal detector and irrespective of whether you are digging. Even “eyeballing” and “beachcombing” require the permit since “searching” is restricted if you have “an intention to find”.
There are two types of permit. The standard permit costs £96 for an adult, is valid for three years and allows you to dig to a maximum depth of 7.5 cm (~3 inches). You can also get this permit for £42 with a one month expiry, but it’s only valid for a
single visit on any day within the month (from date of purchase).
The other type of permit (commonly known as a “Mudlark’s Permit”) allows you to dig to a maximum depth of 1.3 metres (~51 inches) in certain parts of the foreshore. To qualify, you need to have been a member of the Society of Thames Mudlarks for at least three years and able to demonstrate a history of reporting your finds to the museum authorities. The number of these permits is strictly limited and there is currently a waiting list for membership admissions.
You don't need to be a British citizen to apply for a permit but, the nature of the system is that a visitor would be unlikely to get a "Mudlark's Pemit". Also, if you are visiting from another country you need an export license to take archaeological items over 50 years old out of the UK (obtainable from the Arts Council). It would be fair to say that restrictions would be unlikely to be enforced for most casual finds. Also note that "finders keepers" for lost modern items of value does not apply in the UK if there is a prospect of finding the original owner (your obligation to avoid the possibility of being charged with "theft by finding".)
For both permit types, you have an obligation to report finds which might have archaeological significance (to the Finds Liaison Officer at the Museum of London). The legal requirement to report items covered by the “Treasure Act 1996” (within fourteen days of finding) and any consequent implications for ownership/reward apply in all cases.
