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Sorry, I've missed a bit out Dot. I've found his parents and grandparents on 1901 Census. By 1911, I can only find him (he is in a children's home at Mile End by then) and his dad (who is working at a hotel in Bradford as a kitchen porter). Can't find mum - yet (she was german too).
Family gossip states that he was repatriated during WW2. At the repatriation tribunal he says he does not want to be repatriated (and why would he, he came to this country at the age of 1, and I doubt his german was very good if he was placed in a children's home between 1901 and 1911). There is a further record concerning him but it is closed due to the sensitive nature of the information contained within.
His wife did have another child in 1942, not sure whether he is the father or not - only just ordered the birth certificate. I rather suspected that whether he was repatriated or not, he left the family to make things easier for them, since I have no doubt there would have been massive anti german feeling in Glasgow. Even though his name was "anglicised" by then, he definitely had an "illegal aliens registration card" so people would have known.