Can a UK Resident ('limited right to stay' (Consultant under HSMP(from Russia))) work in Germany?

The person is currently working as a Consultant for one of the major UK technology companys. They are now looking to take up a new ignment in Germany within the next few weeks. I'm therefore seeking evidence of their 'right to work' within another EU country, other than the UK (although contract will be issued by a UK registered company). If anyone can offer advice, perhaps guide me to relevant information, I would be most greatful !!