Brompton M3L owner,
I use a combination .. Ergon GP3, short, labeled as the for grip For 2 grip-shifters..
they each have a clamp bolt.. 1 bolt locks on bar end and grip.

they dont come all the way up to the band that holds the brake and shifter on,

so I fill the roughly 3/4" of space in with a wrap of cushioned tape ..

though a more common round grip could be cut down to a ring, just wide enough to fill in that gap, as well ..

any longer bar end and the fold will need the grip bolt loosened .


22.2mm (7/8") is more likely than 22.5mm.. the older , 90's Mk 2 Brommy bar was larger ,
it's shiny with a sleeve in the center, 15/16" tube , off the center

the current bar is matte and anodized .. and bulged in the center ..

you might like these without the bar end ..http://www.ergon-bike.com/us/en/product/gp1

get the short 2 grip shift version..