German-UK double taxation

Hi, I live in the UK permanently (and am a British citizen) and I work as a freelancer online. I've done some freelance work for a company in Germany this year (remotely from the UK). They recently told me that I've reached a certain earnings threshold with them this tax year (which runs Jan-Jan in Germany), and as a result, they'll now have to start taking German income tax from the money I get from them. To avoid being taxed twice in Germany and then the UK, I've been told I have two options: 1) Get a certificate of residency from HMRC and send it to the German tax office. They'll then hopefully give me a document that I can send to my client to prove to them that they don't need to tax me in Germany. (This is the option my client mentioned). 2) Let them tax me in Germany, then claim (at least some of) the tax back from HMRC when I do my self-assessment. I read on the HMRC website that the option you choose depends on the double taxation agreement that's in place between the two countries in question. The thing is, I tried to read it and am none the wiser! Which is the right option in this case, please? Thank you!

Hi,

On the basis of the information you have provided, you should apply for a certificate of residency in the UK and forward it to the German tax authority.
Details of how to apply for a certificate online are provided here:
How to apply for a certificate of residence to claim tax relief abroad

Thank you