Under European Regulation EC 261 of 2004, if you were denied boarding or bumped from a flight, you may be eligible for denied boarding compensation up to 600€.
Usually, the airline may rebook you on an alternate flight, and if it delays for more than 3 hours, you might be entitled to flight delay compensation under the EU law.
Overbooked flight with Easyjet? Were you denied boarding of your flight? Here are your rights
The regulations in the UK are very similar to those in the EU.
Check your compensation online.