Dreamt is often described as the British version of the word (1, 2, 3), however, a Google Books Ngram search shows that dreamed is more common than dreamt in both British and American English. Still, dreamt is on more equal footing in Britain than in America:
People use dreamed about 2.5 times more often than dreamt in British English, but about 7 times more often than dreamt in American English.
You can use whichever word you prefer, but dreamed will probably be less distracting to your readers.
Source: Grammar Girl