More specifically, by “Asian” Brits mean “someone originating from the Indian subcontinent”, so it could mean Pakistanis (mostly muslims) or Indians (mostly Hindus). There are significant minorities of both in the UK, largely because of the country’s colonial past. The Brits use the term “orientals” for the folk Americans refer to as “Asians”.
Don’t ever refer to Chinese, Japanese, etc., as Oriental. To them it’s as bad as whites using the n-word.