The Connexion newspaper touched on this last month. I seem to recall a year's free extension is available if your passport has spare pages upon which the endorsement can be printed. Or if a journey becomes essential while the old passport is away in the UK being cancelled and replaced, a temporary travel document is available from the British Consulate - though you have to go there to get it, and there's quite a hefty fee involved. I believe the process varies according to whether the passport holder has already booked flights/crossings or is planning to. Best ring the Consulate to find out how it all works. Hope this helps. Maybe someone who still has the newspaper could add to it.
C of Caylus
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