is apparently “learnt” in UK English. Check these 500 pages of references in the BBC archives.
I noticed it when I was reading. I wondered if that is an older conjugation. I was not able to find “to learn” listed as a weak verb in Old English with a “t form” ending.
However, yahooanswers thought the same was probably true, but argued it using German. That’s odd.
In the Word Reference Forums they say that “learnt” is preferred in UK, learned/learnt is equal in Canada- but learnt is not often used, and that in the US “learned” is considered educated while “learnt” is considered hick.
It doesn’t give me a definitive answer on whether learnt is an older form of the verb or a newer one, but… I guess it doesn’t matter to anyone but an English teacher or a foreigner trying to sound reasonably smart in the US.