Richard Rawles writes:

Dear David Meadows,
In fact UK nationals *can* still sign the petition at <http://petitions.pm.gov.uk/AncientHistory/> as well as inspecting the list of other signatories. Perhaps you could correct this? It would be a shame if people who would have wanted to sign didn't...

... apologies for any confusion; if you are a UK National and haven't signed yet -- to use one of my father's phrases, "Don't wait for spring, do it now!"