The Competition Commission has rejected the proposed merger of block maker Thermalite with H+H Celcon because it may operate against the public interest. Thermalite will remain part of Marley Building Materials. <p></p><p>H+H Celcon agreed to buy Thermalite in December for an estimated &amp;£81 million but the deal was subject to approval by the competition authorities. </p><p>The combined operation would have held 21% of the block market. </p><p></p>