Travel documents are issued to refugees based on the Geneva convention of 1951 or to stateless persons based on the convention of 1954. If you hold a travel document issued by Germany and want to travel to the United Kingdom you will need to obtain a visa first with one exception:
you are married to a EU citizen who has made use of his rights to live and stay in another EU country and you are travelling together.
http://www.ukba.homeoffice.gov.uk/siteco… [read page 5]
Should you hold a German EU passport which is often referenced to as travel document too, you will not need any visa for travelling in the EU, just your passport or the German ID card.
http://ec.europa.eu/youreurope/nav/en/ci… ..