UK citizens and citizens of states that joined the EU prior to 2004 are free to work in the UK without restriction. Citizens of states that joined the EU during or after 2004 are entitled to enter and live in the UK, but there are different rules regarding their eligibility to work here.
Citizens of Bulgaria and Romania need permission to work here, and have to apply for permission to the UK Borders Agency (there are different rules relating to seasonal agricultural work, however). Citizens of the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Slovakia and Slovenia need to register to work here, if they wish to work for longer than one month. The UK Borders Agency
website has all the information needed for potential employees wishing to register or apply for permission to work.
As an employer, you need to be aware that you could be fined up to £5,000 if you employ one of these EU citizens if they have not applied for permission or registered to work here. You should not employ them unless and until you have seen documentary evidence to confirm their eligibility, and you should take a copy of the documentation and keep it safe.
In order to avoid claims of racial discrimination, you should always check the identity of any potential new recruit and keep a copy of the documentation that proves their eligibility to work in the UK. For British citizens and citizens of EU states that joined before 2004, that could simply be a copy of their passport. For citizens of newer EU states, that will be a copy of their registration form or permission to work certificate.
This is a complex area and I would always advise you to
contact me if you are ever unclear about your responsibilities.