I found the treatment fair from the HR Taxoffice back at the time when I was liable to UK Taxes. The poor Germans asked me to pay the diffrence Tax between the UK and the German tax as I paid not enough in the UK according to the Statement provided to the Germans back that time. The linear taxation gave me more Net in the UK and the Germans took another crop. I did not consult the double taxation agreement between UK and Germany back at the time and lost some serious money one time to the Tax Office in Germany, they lost a few months later a Taxpayer = I moved out of the Country and continue to contribute to the UK Tax.
http://www.hmrc.gov.uk/taxtreaties/in-force/germany.pdf
That link should give you the recently uodated agreement between UK and Germany for example. Employment is also mentioned there, Art. 14 / 3. I consulted also other double taxation agreements between EU-Member States and others and there are often provisions for "Crews", named Seamen and Aircrew...
It is clear that people have to pay some tax somewhere. Try to stay legal and you benefit as well from existing rules and regulations. To evade Tax will get you into trouble one day, some sooner, some later.