Kilmarnock chairman Michael Johnston has defended his club against criticism for calling off the Aberdeen clash at the weekend because of a frozen pitch. The SPL have written to Killie demanding answers as to why their undersoil heating system failed to prevent the cancellation.

"We have a sub-air system, which is unique in Scotland," said Johnston, who pointed out it is almost six years since the club last had to postpone a game.

"It is an American system and West Ham are the only other club to have it. The sub-air system blows the air into pipes under the pitch. The pipes have holes in them which allows the air to percolate up.

"We then put ground sheets over the pitch and, with the bed of hot air, the sheets rise two feet above the pitch. That keeps the frost out.

"It is more of a frost prevention system. We had a prolonged period of frost and it was already in the ground by Saturday. Once the frost is in the ground, it is hard to get it out.

"The sub-air system is fantastic for keeping water off the pitch. We never have any problems with a waterlogged pitch. The weather forecast for late last week was for higher temperatures and rain.

"We were waiting for that milder weather to arrive. That would have removed the frost and the pitch would be fine.

"Some milder weather did come and if it had been inspected on late Friday afternoon then the pitch would have been fine, but there was another drop in temperature overnight and the frost went back into the pitch.

"We shouldn't have relied on the weather forecast but, then, everyone does. To prevent the match being off, the system would have had to have been on for 10 days before, because it was on the Wednesday of the previous week that the hard frost arrived. It is widely acknowledged that we have the best surface in Scottish football."