No union jacks etc are permitted.
The rules on that changed a few years ago, you are allowed certain flags now.
Which fonts are UK road legal?
The only legal fonts in the UK are UK Legal, UK Legal 3D, UK Legal Carbon GEL RESIN and UK Legal Black GEL RESIN.
Which badges are UK road legal?
The Badges that are road legal are the Country Badges eg:
GB Euro, Union Jack, Wales, England, Scotland, Isle of Man, Ireland, and Northern Ireland.