Upvote:18
You're British, so you have the right to live and work in the UK*. Entering the UK using a Canadian passport doesn't change that. There's no need to "validate" anything, so I'm not sure what the border officer would have been talking about. Any conditions on leave stamped in your Canadian passport don't apply to you.
*By "I'm British" I'm assuming you are a British Citizen, not one of the other kinds of British national.