Unibet is offering UK residents a free bet bonus up to a maximum of £20. In order to receive the free bet you need to register and deposit at least £10 and Unibet will immediately match it.
Unlike most bookmakers, the bonus is literally that so you can use it, or portions thereof, on any selection you like. The only thing to note though is that before you can withdraw the bonus money you must turn over the bonus six times in the Unibet sportsbook by placing bets at odds of 2/5 (1.4) or above.