A heads up.
As from 8th April 2015 (today) the UK will start checking passports for people leaving the country. The Schengen Area has always checked passports/ID cards for travellers entering AND exiting, but up to now the UK has only checked people arriving, not leaving.
As this requires extra desks at airports, ports and St Pancras station I imagine it might cause a few minutes delay until the system beds in.
The official government announcement is here: https://www.gov.uk/government/publications/exit-checks-on-passengers-leaving-the-uk/exit-checks-fact-sheet
Sorry I didn't post this on the correct forum, there is no UK forum!