Definitive Answer - The latest Shabbat goes out in London is 10.28pm (as per the week in question). This is based on the times by the London Bet Din, the leading mainstream authority. Therefore, technically, a 10.30pm departure does not break the rules. The preparations beforehand are a separate issue but do not fall foul of the 'flying on Shabbat' rules.

Hope that brings some clarity.

Fred