Welcome to FT

As others have said, the sticky is full of loads of useful information. A search of the forum (or just looking back a few pages) will also give you a lot of help.

From my personal experience last year I would recommend you have a look at starting in Scandinavia. For me it was a toss up between Sweden and Denmark, and I eventually started in Stockholm. I haven't looked at the spreadsheet (linked in the sticky) for a while but I'd imagine it is still much the same. I booked direct with SAS and collected the tickets in Stockholm. The key point being that you have to physically go there and buy the ticket, if you go to an agent in the UK you will pay the UK price. The only exception to this is if you use travel agencies in Canada, but that's another topic you'll find many older threads about.

Bear in mind that it also depends on what class you are planning to fly in. My example (and many of the others you will find) are based on flying business class. If you're flying in economy then the UK is (or was) pretty much the cheapest place to start from anyway.