Export licenses are required for any important artefact or antique subject to the rules here. http://www.artscouncil.org.uk/export-controls/export-licensing
It's basically designed to ensure that national treasures don't get sold abroad when there is a good case to be made for keeping them at home.
The Coenwulf gold penny was a good example of the licensing system in action as it provided for funds to be raised at home to ensure that the item didn't leave the country.
I'll post this here seeing as my original thread got ganked by a business tout
I only know of 1 other that is because I owned it. But sold it on a few years back. Been actively searching for another in a really nice grade but alas so far have not found any and this one is the only one I have found in the few years gap. Unlisted variety and should really be confirmed as I owned this and 1 other. Obviously quite rare 1826 Half Penny with Roman I for 1
A Friday afternoon job. MA over FR, though the M is also blundered and entered twice, the G possibly with either a flaw or over the left side of an M, the following R made from a couple of misplaced Es which were reinforced to form the R and F of FR over an E. Apart from that it's fine.