Some of the individual sections are probably still hand-brazed, but joining the two main triangles is computer controlled:

Brompton has developed a thermographic PLC-controlled autobraze machine to braze the two parts together. It delivers reliably consistent quality on an extremely critical area of the bike. This machine was designed and built in-house as the UK supplier went bust. It took two years and an investment of £160,000 to create, but it delivers the goods and would be next to impossible for a competitor to replicate.