Howard Wilkinson’s ‘Riddle-Me-Ref!’

Howard says, “See if you can work out the name of the top-flight referee from my series of cryptic clues!”

“My first is in kettle but not in pot,

My second is in rope but not in knot,

My third is in summer but not in spring,

My fourth is in slide but not in swing,

My fifth is in petrol but not in oil,

My sixth is in ruin but not in spoil”