You’d need a long circ to knit, for sure. And yes, you would knit back and forth with it rather than in the round. You could also add a crochet edge, if you know how to do that.
There must be places that ship to the UK that carry long needles.
Here is one. I just Googled UK knitting stores and came up with a long list.
And I am currently trying to teach myself to crochet… and that’s a whole new topic in itself… it’s crocheting into the foundation row, get’s me into a muddle every time!