Katharine Handel

Hello, Is there anyone here who can give me some advice about a letter I have received from the German tax authorities? I do some freelance work for a university in Germany and I received a letter asking me if I am liable to pay tax in Germany on this income. I'm a UK resident, am self-employed, and do my taxes via Self Assessment every year, so I'm pretty sure that I am not liable for taxes in Germany. I have a dual tax certificate that will hopefully prove this. However, the letter also asks me several questions about the income and I’m not sure whether I should answer them even though I don’t think I need to pay anything. Has anyone else ever had a letter like this who could advise me? I would be grateful for any help. Thank you.