Refugees were not allowed to join the British Army until early 1943.  This policy changed when the British government accepted that many of them had skills and experience which could be useful to the war effort. A couple of dozen young Jewish men who fled Nazi Germany (several on the Kindertransport) joined the Suffolk Regiment in Bury St Edmunds at this time.  All such refugee servicemen were volunteers, unlike most British men who were conscripts. 

Once in a fighting unit, such as the Suffolk Regiment, refugee servicemen could be deployed in battle.  For their own protection, the British army gave Jewish refugees the option of anglicising their names and identities - a precaution in case they were captured by Nazis.  Some refugee servicemen went as far as changing their religion as written on their on their army pay books to ‘Church of England’.   It seems that these measures to disguise refugee servicemen’s true identities were optional,  Often, they were given just a few minutes to decide what their future English names would be.  Many chose new names similar their old ones e.g. Rudolf Reitmann became Robert Raymond.

After the war, refugee soldiers did not automatically become British nationals.  It was not until the late 1940s that most of them – provided they had stayed in the United Kingdom – were granted British nationality.  Almost all of these young men kept their anglicised names.

Sources

Jewish Refugees from Germany and Austria in the British Army, 1939-45 by Steven Kern, University of Nottingham, June 2004, available at http://eprints.nottingham.ac.uk/12964/1/403319.pdf

www.jmberlin.de/en/new-names-friendly-enemy-aliens-britain