Either way, £120 seems like mad money for a Surly fork.
Admittedly I can't find any examples of the canti only one but there's been a couple of the curved leg disc and canti ones sold on here for £75 and one on ebay that sold for £50 recently.
I've never paid (nor gotten) anything over about £70 for a Surly fork and I've bought and sold quite a few... 1x1, Steamy and Crosscheck forks over the years. Sub £50 is pretty common.
If you're willing to look at other brands you should be able to pick up a fork that does everything the Surly fork does (with the proviso of slightly less, but still plenty, tyre clearance) for considerably less, like you could have £100 change from that £120 budget.