In British English,is the word "used" with Past Simple?For example,"I just bought a house".
I think there is a word missing from your question. Did you mean "Is the word "just" used with the past simple?" If so, then yes. It might not be everyone's choice to denote something that happened very recently but you'll hear it a lot.
I just ate the last cookie.
I just bought a car.
I just dropped a glass and broke it.
It is, of course, perfectly possible to say:
I have just eaten the last cookie.
I have just bought a car.
I have just dropped a glass and broken it.