There was a question on the U.K. Detector Net the other week re gold finds. Not on that forum myself but it seems not many have found gold and of those that have, with one or two exceptions, have only found two or three which seems pretty poor.
No reason not to declare finds in the U.K. as you either get them back or the value (granted I've had had finds that dealers have offered double the initial Treasure Trove valuation).
Treasure is coins/items over 300 years old with at least 10% gold or silver and at least two of them in the area. If less than 10% precious metal then there must be at least 10 to come under the provisions. So you can find many single gold coins in different/distant areas without worry.