Why would TfL specifically get involved? It's more likely this is an issue for the ASA, on account of it appearing to use the word ‘FUCK’, which is hardly controversial.
Transposition vs substitution; I'd say F*CK is more likely to suffer the ASA’s wrath than FCUK. But who knows, need more details to be sure of anything.
You would say transposition vs substitution but there a few different string metrics. I picked one of the most popular which treats substitution as the same as transposition.
It shouldn't be hard to argue and force them to disclose what string metric they are using and what distance is the minimum if you're prepared to take them to court.
How did this reach the front page of hacker news!? This is nothing more than an advert for sending money overseas. Oh and for the marketing team running this blatant advert, here's a free tip that will help your SEO a bit, add a 301 redirection on your non-www site. You don't even redirect http://transferwise.com to http://www.transferwise.com
Then, bitcoin appeared, thanks to which you can send money to many countries for free (or even with a small gain on exchange rate, if youre lucky).