There could have been traces of the drug on their cases/clothes that would have been picked up by sniffer dogs. Better to seek advice rather then forfeit your freedom!
Other games:
West Brom v Arsenal
Swindon v Chelsea
Tranmere v Stoke
Watford v Norwich
Aston Villa v Tottenham
Hull v Huddersfield
Leicester v Derby
Birmingham City v Swansea
Fulham v Everton/Stevenage
They've put that as a front page article on their site and are discussing it sensibly. A real refuge of the damned! All credit to them for managing to maintain their sanity.