you need new holders and pads, the brompton 1 piece pads are 1 piece so have no inserts. The old / current brompton pads with holders/inserts, take the BXP inserts no problem
I recently scored some Ultegra pads/ holders for my Brompton - heavily discounted from Chain Reaction - hopefully the bolts on these won't rust as quickly as the original Brompton ones did.
just for clarification, you can swap out the brompton brake pads with the swiss stop BXP's? So you just need the pads and not the and holder?