Supply problems are most acute with aircrete blocks as raw materials used in their manufacture run dry.

The blocks use pulverised fuel ash (PFA) as a raw material which is a by-product of coal fired power generation.

Gradual closure of coal-fired plants for cleaner energy sources has reduced the amount of fresh PFA.

Stockpiled PFA is still available in huge quantities.

But the older material doesn’t have the same performance characteristics as fresh PFA so manufacturers are having to adapt their production processes.

Calum Forsyth, managing director of manufacturer H+H said: “The inevitable result is a short-term pressure on supply.

“While H+H is able to utilise stockpiled PFA we have had to accelerate the development of our production process to accommodate the different characteristics of this raw material.

“As with any significant change to manufacturing, this has required considerable adjustments to ensure quality of the finished product is acceptable.”

“The net result is a reduction in yield.  While our plants are still producing around 30% more volume than was the case four years ago, we are facing pressure to supply the growing demand.”

Forsyth said this is a “short term difficulty” but warned that regular customers would be favoured while shortages continue.

He said: “In the immediate future we are focusing on directing all of our output to the customers with whom we have long-term supply contracts in place.

“This will mean increased pressure on the spot-market for blocks for those who do not have agreements with H+H.”