Sounds like a nice way of saying that trading in their shares has been suspended. CREST is an electronic settlement and registration system.
Added: I believe that CREST was also the old name for the European Research Area and Innovation Committee (ERAC), an intergovernmental policy advisory group, whose origin goes back to the Marechal Group.
It also seems to be a UK-based consortium of research groups in small new universities -
CREST | Consortium for Research Excellence, Support and Training, as in Old..rrified's acronym.
However, as the Pegasus website notes that withdrawing from CREST might interest their shareholders more than EU science ministers or small universities' research departments, I suspect it's share-related rather than research-related.