There is one confirmed London date on the Spook Country promotion tour:
An Evening with William Gibson - London, Tuesday 28th August 2007, 7pm, (TUC) Congress Centre, Great Russell Street - tickets £7 via Blackwell booksellers telephone line +44(0)845 456 9876 Mon - Fri, 9.30am to 6.00pm
However, so far, the rumour of a lunch time and / or evening signing the next day, Wednesday 29th August @ the Forbidden Planet bookshop cannot be confirmed
The signing events section of the Forbidden Planet website has been recently updated with some September signings of Dr Who books etc., but there is no mention of William Gibson.
I went physically to the shop today, and enquired of the helpful and usually well informed counter staff, who checked with their backroom colleagues as well, and none of them had heard of any planned William Gibson signing at Forbidden Planet
There are no Penguin or Forbidden Planet in-house printed posters or leaflets on display even about the publication of Spook Country on 2nd August in the UK (according to Amazon) or 7th August in the USA, let alone anything about any signing or author reading event.