(Disclaimer, I do 50+ of these deals per month in the USA, so that's the context I'm speaking from. You should connect with a local RE Attorney, but I can give you some context so you have a more meaningful discussion)
Don't ask the bank. They will tell you "no" if you ask. In most loans transferring title without paying off the existing loan is a default (hence the dreaded due-on-sale clause). HOWEVER, if they're getting paid, there's an extremely low rate of those loans being called due.
In your case, I'd be looking at creating a "wraparound mortgage." You can mark up the interest rate and make a profit on the existing loan as well!
Alternately, you can do a hybrid deal, where you create a separate, 2nd position mortgage for just your equity, while the first mortgage is taken subject to, and the buyer effectively makes 2 monthly payments (one to the bank, one to you).
I just wrote an article to simply explain wraps: https://www.biggerpockets.com/member-blogs/15497/102003-wrap...