Registering your arrival :
Greece
Registering your arrival
As an EU national you do not need a work permit to work in Greece. However it is always best to be prepared, and have employment set up before you go.
Although there is no need for a work permit, many employers are not yet aware of this fact or at least pretend not to be! Some employers will attempt to con you into believing that if they hire you without one, they are taking a huge risk and as a result, will attempt to pay you less...
If you plan on staying in Greece for more than 3 months, you will need to get a residence permit. Failure to do this could result in your having problems leaving the country and also you could be prosecuted for contravening the regulations. The application for this must be made in person, prior to the expiry of this 3 month period, to your local Aliens Department Offices.
If you know in advance that you plan on staying in Greece for more than 3 months, then it is advisable to get a "Change of Residence Certificate" which is issued by the Greek Consulate in the UK before you leave. Also be aware that the Consulate keeps records of British Nationals living in Greece, so you will need to register yourself as living there too.
Expat Focus - Residency
Foreign Office - Registration of residents