The Lincolnshire-based company won the rating by using Super Spacer from Edgetech IG Inc, which claims to be the world’s only all-foam, no-metal, edge-seal product line that provides maximum condensation resistance, durability and energy performance.

A spokesperson for market analysts Michael Rigby Associates said an “E” rating was the current standard, with a “D” rating required for new properties under revised Building Regulations.

George Barnsdale managing director Stephen Wright described achieving an “A” rating as “a golden opportunity” for the company and for the timber window industry .

“As legislation looks to be tightened, and more demanding in terms of energy efficiency, we can give our commercial and public sector customers what they need to future-proof the buildings they work on,” said Mr Wright. “I’d like to see other timber manufacturers following suit to help develop the market for sustainable energy rated windows.”

The company intends to put its sliding sashes and inward opening windows through BFRC testing over the next six months.