Deutsche Bahn doesn't manufacture rolling stock. They buy it from Siemens, Stadler, Talgo, Alstom etc...

Edit: AFAIK, some of it - mainly high-speed trains - is designed according to DB specs and subsequently offered under a new name (and with changes) to other train companies. For example DB ICE 3 (manufactured by Siemens) / Siemens Velaro.

Incorrect. They wouldn't fit in the tiny UK loading gauge (profile). UK trains are indeed variants of continental models, but made to custom size, and many (most?) of them in the UK.

> The UK buys most of their trains from Deutsche Bahn (German Rail) and just brands them differently.

This is totally incorrect.

We buy our trains from French/Swiss/German/Spanish/Belgian manufacturers, or build them ourselves in eg Derby.

We do not buy our trains from DB.