I just sold my Brompton (titanium frame) bike. Maybe I should have looked at putting an e-bike kit into it. In the back of my mind I seem to remember seeing that Brompton themselves offered a kit. I could be wrong though.
Have you checked to see if there's a specific Brompton section here (I haven't). EDIT: Just checked, and yes, there is a dedicated Brompton section.
I just got my first e-bike yesterday after more than a month of research and testing. I'm super excited and it is certainly going to make my 30+ km commute (each way) a lot easier.
@Cheryl p you can check to see if your bike frame is compatible with the Bafang mid-drive system, many vendors sell complete kits, fitment info here. If you're a DITY person you can save yourself several hundred dollars doing the e-bike mod yourself.