On: Britain is the most corrupt country in the world?

[dang]

That's a much stronger claim. Arguably doesn't mean what it says; it's more like a slightly weaker plausible.

[paulddraper → dang]

Definition of arguably: "it may be argued"

If a position can't even be argued, you necessarily must assert the opposite:

"Britain is not the most corrupt country in the world"

(or phrase it as a question and invoke Betteridge)