What to expect for flat hunting in London

Hello everyone. I was wondering if anyone could provide some info regarding what to expect when flat hunting in the UK/London.
My concern is references - would agencies or landlords accept Canadian employer references? I currently live at home in Canada and am not renting, so I am unable to provide another landlord reference. Will this be a problem to secure a flat? I have a couple thousand pounds saved - would they accept paying a few months of rent in advance if I do not have a UK reference or any sort of landlord reference to provide them?

Also, would you advise to have a position lined up prior to flat hunting? (Stupid question I guess)

Any advice would be appreciated!!!

Many thanks!