OK, can we have a terminolgy check here. Is this a UK licence issued in accordance with JAR FCL and contains the section inside that by virtue of JAR FCL1.15 the priviliges can be excercised in any member state or are you referring to an older UK issed ATPL issued in accordance with ICAO?
If it is a JAA licence then they have to accept it. If it is a UK CAA ICAO licence then you are peeing in the wind. However you can convert a UK CAA ICAO licence to a JAA FCL licence and thus an EASA licence by paying the dosh to the CAA.
If they are refusing to accept a JAA licence then you need to contact the flight standards guys at EASA and ask them to intervene.