Since you've asked for personal experience, let me answer although the question has been asked some time ago.
I am German; the first time I have travelled to London was in 1975, after becoming an adult, [yes, you needed to be 21 years to travel on your own by that time] and all I had with me was my "Bundespersonalausweis" [Federal ID Card].
By that time it was a booklet, half of the size of a passport, which fitted into the wallet. The picture was glued, rivetted and stamped. Nothing has changed from then, citizens of the EU/EEA still can travel within the EU on their national ID cards, however nowadays they are laminated cards with digital photographs, still in wallet size. It is planned to issue a new type by the end of 2010 which will be credit-card size and will include a microchip.
Some British people here think because they need a passport to travel to the continent everybody else needs one to travel to the U.K. but that's no true. Brits need passports simply because they do not have national ID cards at present.
Let me still add another link of your government.
http://bia.homeoffice.gov.uk/travellingt…
If you check "What documents are accepted at the border" you can read:
"We also accept national identity cards for EEA citizens."
And also a link from passport service on the new U.K. ID cards which are hated by most people.
http://www.ips.gov.uk/cps/rde/xchg/ips_l… ..
If you check the document requirements of Ryanair [which requires British people to have a passport on all flights] you can read:
The only forms of travel documents accepted on Ryanair flights are:
• a valid passport
• a valid National Identity Card issued by the government of a European Economic Area (EEA) country. (Only the following EEA countries issue National Identity Cards acceptable for carriage on Ryanair flights: Austria, Belgium, Bulgaria, Finland, France, Germany, Gibraltar, Greece, Cyprus, Czech Republic, Estonia, Hungary, Italy, Liechtenstein, Lithuania, Luxembourg, Netherlands, Malta, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland)
http://www.ryanair.com/site/EN/faqs.php?… ..
I wish some people like "Ian M" or "froggeque" would take the time and read through the answers and links other users are providing instead of repeatedly providing the same wrong statements!