Anyone flying/working, wether you are contract or employed through an agency such as Brookfield or Rishworth, for easyJet, Ryanair, Veuling etc thinking that they can avoid paying tax in the country where they derive the majority of their income are just plain stupid or very badly advised.
It is the employees responsibility to contact the tax office in the area where they work. Don't ever get misled into thinking that the company you work for has any responsibility to pay the unpaid tax, they don't. Their resposibility extends only to NI contributions and PAYE if such a scheme exists. This ruling applies to all nationalities of the OECD, (effectively everywhere!) so if you are French working in Spain or Italian working in England or English working in Germany, the rules apply to you too.
Just because you become non-resident for tax purposes in one country does not excuse you from paying tax in the country where you work.
I would be very surprised if the authorities in Germany are only collecting the unpaid tax from the 1st of this year .They have the authority to collect tax for the previous seven years. They can also apply a penalty equal to 100% of the unpaid tax. Think Boris Becker and Michael Schumacher, both who narrowly avoided going to jail for just the same thing.
There is a very easy way to tell if you are liable for tax.
Ask yourself this simple question; am I happy for the tax authorities in the country where I work to know all about my financial arrangements?
If you answer NO, then you are breaking the law in that country.
My advice to you, if you are avoiding tax where you work, is to contact the tax office and come clean, before they apply the punitive fines when thay eventually find you.