After thinking about the problem again and again I decided to change my brake unit to the better. I learned from the bromptoneer forum that it is possible to put V-brakes on a Brompton.
I asked an experienced cycle manufacturer who was able to carry out the necessary work if he could help me. I found the craftsman I looked for in Edermünde-Holzhausen.
We made an appointment for the following Saturday. I cycled about 42 kilometres with my Brompton in heavy rain to get to his workshop.
The helpful craftsman recognized the issue at once and started right away to take measurements of my Brommi.
He came to the following conclusion. Further with the prospective thumbs