% speed derailleur geared Brompton..
 

I have just bought a 5 speed derailleur geared Brompton on Ebay..Does any have any suggestions as to how this was done..The rear dropouts are the standard size but the wheel is dished on the right side..a long cage Shimano derailleur is used..I think it is a freehub but may not be?

Pictures for proper analysis are needed.

many inventive things have been done to Brompton's format. aftermarket.
like sticking a front derailleur on so dual range on 3 speeds

"standard" as that has widened over the years. 5 speeds were on 120 axles
now 130 is the normal width.

current bikes offer 6 speeds by having a 2 cog cassette on a 3 speed internal gear hub.