According to the passport office - it says that you can apply for a British passport while visiting the UK. The cost of course is less & would probably be quicker (they're saying 6-weeks on the website for
UK applications) - so, maybe not worth it seeing its your first passport & with rule tighting.
I would apply from here - apart from the cost difference, why have all the hassle
Read all in the link below, about half way down it appears to apply to your question
http://www.direct.gov.uk/en/TravelAndTr ... /DG_174098Since you probably have close relative living there (mentioned in another post) you'd have a UK address & phone number. I think rules have changed a bit & now relatives can countersign - if not then is there anyone else in the UK you know who is a Brit or commonwealth citizen that may do it for you?
Remember to have not only your certificate of registration but also your long form birth certificate + back up mothers long form birth certificate & marriage certificate - it would be just in case they get snotty
Without that Brit passport, the border folks I believe wont admit you as a Brit even though you have the certificate of registration + Canadian passport. You'd be on a 6-month visitors visa.
Again, suggest that you apply for our Brit passport from this side of the atlantic. You've waited so long to get to your British citizenship, so another few weeks on top of that for the passport wont IMO be too hard on you.
Trust this is what you're looking for
Disclaimer: I am not an immigration expert & anything that I post on visa & immigration is based soley on more than 30 years of personal experience & interaction with the UKBA & Home office.