Which should make it a piece of cake to put together a UK-ready version - 50Hz transformers are far nicer beasts to work with than 16⅔Hz transformers.Dual voltage tram trains of a suitable type already exist in Germany on the Karlsruhe Stadtbahn, although they are designed for 15KV 16.7Hz AC and 750V DC operation.
I have found som information unfortunatly only in German at http://de.wikipedia.org/wiki/GT8-100D/2S-M
The exact voltage of the DC system doesn't really make a difference to anything, a well-designed tram can be converted from one system to another in a few hours.