Can you travel in the U.K with a Greek ID?

Many of my friends have told me that you can indeed travel with your national Greek ID in countries that belong to the EU without your passport. I will be traveling to London in less than a month and I don't have a passport. I've read some other topics, in the Greek ryanair forums, and I saw that most people had no problem boarding just by showing their ticket and Greek ID. Do you know anything about it? has anything changed as of late?

Thanks.