No it�s not just as American thing, the so-called �double jeopardy� principle also applies in the UK. The principle means that where a defendant has been acquitted of a particular crime, he/she cannot be re-tried at a later date for the same crime even if new evidence arises (this is obviously different from the question you�re posing). However, the Law Commission is looking into whether the principle should be abandoned in certain murder cases where �compelling� new evidence comes to light after a suspect has been acquitted. The LC review was prompted by the Stephen Lawrence case. It�s also been prompted by the fact that developments in scientific techniques means that fresh, reliable evidence may now be obtained today in respect of a murder that happened, say, 10 years ago, but which science at the time was unable to provide (and, hence, the defendant was acquitted through lack of this evidence).