Originally Posted by
LondonElite
As a citizen of the EU, you will have whatever work/volunteering rights in the destination EU country regardless of the nature of the document you used to enter.
I would still recommend using the EU document to enter the country. It simply makes no sense to use a non-EU document if you can use an EU one. As an EU citizen you enter the UK as a matter of right, they can't turn you away, they're not even supposed to ask you any questions such as "how long are you staying?"