coolbeans
Do you not have Union representation? If you have, then they are the first port of call to get this resolved. 20 minutes in 6 hours seems a little low - where does the "legal requirement" come from? Might also help if you can find out if there are any EU guidelines on the subject - they seem to have issued guidelines for just about everything else!
Being unlicensed, we do not operate to the same rules and regulations as the ATCOs at LL. Our working agreements are negotiated by our Union (PCS), and the relief time granted under the current arrangement seems reasonable - a bit more (but not substantially!) than 20 minutes for 6 hours.