Lots of Brompton folks use Ergon grips. I myself have a pair of Ergon GP1 biokork (grip shift version) in size Small. There are several threads discussing these. Ozonation even started a step by step thread on how to install Ergons.

Those Brooks grips should fit since the inner diameter is 22.2mm and so are the Brompton handlebars. And if scroll down in the link you provided, several reviews/comments from Brompton users too.