Do I have to enter the UK on my UK passport?

I am a British subject with the right of abode. I had a British passport for a long time but stopped renewing it. I am also a Canadian citizen with a Canadian passport. When I enter Britain, about half the time the customs officer asks me if I am British (coming to a country to visit your sister, for example, will get you asked that) and when I say "well, I was born here", they say "why are you travelling on a Canadian passport?" (which also includes a line saying where I was born.) This is usually a reasonably glary moment that could possibly make you feel the interview was not going well, but I know they have no choice and have to let me in. I say that I've lived in Canada since 1969 and that it got to be too much effort to renew my British passport. Then they let me in.

Disclaimer: I never have any problems with border guys and then someone else comes after me with the exact same situation and has a problem. I'm extremely lucky. I can't guarantee you'll have as easy a time as me. But this is what I do.

If you hold more than one passport, you're supposed to only be consistent with what you do in a country. So enter on one, leave on the other is a no-no, but you're fully entitled - as a US Citizen, to visit the UK.

I did the same when visiting South Africa - my friends were in the 'tourist' queue, and I had both passports with me, but went through the foreigner queue with them rather than use my SA one, purely because it was simpler. I asked the ticket counter when I was leaving whether it would mean I had to do anything different, and she said as well that it happens a lot, and that you just need to be consistent.

Otherwise if you use one to get in and one to get out, for example, their system could show that the US version of you overstayed - and nobody wants that :)

EDIT

This forum and others point out anecdotal experiences where they or a family member with both citizenships have had no problems. The UK (unlike the US to some extent) is fine with dual citizenship, especially given the scope of the Commonwealth.

However, just a thought, you should realise you'd likely be bound by the law of entering as a foreigner, and possibly not have recourse to public funds, for example - although that part I'm not totally certain on - not a lawyer ;)

It can lead to complications.

Arrive at Heathrow and use my British passport (born there) to skip the lines. But I am departing for another country with its business visa in my US passport (I live/work in the USA)

They check my US passport to confirm the entry visa for destination but can't find a UK entry stamp. Look at me (I'm very white and nerdy) and ask "dual citizen? - "happens all the time, no problem"