http://www.hmcourts-service.gov.uk/infoabout/enforcement/ind... is a good source for England in general. Enforcing elsewhere within the UK is even difficult, never mind the EU at large, although it can be done. The normal approach against an individual is an attachment of earnings order, where the employer withholds money from salary to pay off the judgment (or if unemployed, the same thing happens from the person's benefits), but if the person has no income or assets (or, at least, no assets within the jurisdiction), there's really not very much anyone can do.