Gobstopper has is dead on. Any Romanian/Bulgarian who entered this country after the "Accession date" (1st January 2007) need a work permit to work here. (There was something about being self-employed as a way around this but I'm not too sure about the details).
Other than that, even if they were in the country before that date, they needed to have a valid Work Permit or Green Card on 31st December 2006 to remain/work here legally without them.
They can apply for PPS numbers alright as these are now required for driving licences, council housing, etc, but having one does not automatically entitle them to work or claim SW here.