I have dual Canadian/UK citizenship.... I lived most of my life in Toronto, but moved to London UK from 2008-june 2011. I have just returned to Toronto "For good" where I am sponsoring my boyfriend for perm. residence.
this was my PERSONAL experience:
i LOVED LOVED LOVED living in the UK for the first 2.5 years, thought I would stay there forever then one day it hit me, I need to be back in Canada, where people are friendlier, things are cheaper, you don't live paycheck to paycheck and aren't constantly worried about crime.
great thing about the UK, you can get on a train and be in an amazing magical city/town in a hour or more.... you can travel the entire UK very easily, which I did. you can hop across to europe very easily. I was able to travel europe extensively and cheaply while I was there, which was one of the reasons I stayed so long.
But, I feel much more relaxed in Canada. In London I had an aggressive attitude when riding the tube everyday to work, everyone is miserable, everyone is pushy and you constantly feel on edge. My family came to visit and my mum actually said "wow, you are so aggressive, where did this come from?"
also, a big plus...my boyfriend is now earning DOUBLE what he was making in London and he it incredibly happy here in Canada . (he is Australian)
cost... here are some comparisons for you.
in London we were living in a TINY TINY 1 bedroom flat that was a 10-12 min walk from the tube for £992 per month, plus our £30 per week on the tube, plus food of course.
toronto: large one bed apt with an amazing view of the lake, 3 min walk to subway $1200 and no subway for my boyfriend since ha can bike/walk to work.
the only thing that is cheaper in London is alcohol at pubs and in shops.....
not sure if this will help you at all, but these are some of my opinions.... let me know if you have any specific questions
ps- and yes, you can get marmite in every grocery store here mmmmmm. and bulk barn has a great selection of UK chocolates etc