The Hotspur Mark I was constructed from wood and was designed to accommodate eight fully armed airborne troops. Its wingspan was and it was in length. With a full load (approximately ), it weighed approximately . The Mk I was distinguished from its other variants by the addition of cabin portholes along its fuselage, and hooks on the nose and tail to allow multiple Hotspurs to be towed together. The two pilots, and later the pilot and instructor when the Hotspurs were used as training gliders, sat in tandem in the cockpit. It had a jettisonable undercarriage, and its unusual fuselage functioned like a lid; once the Hotspur had landed, the troops inside would throw off the top half of the fuselage and then climb out of the lower half, much like leaving a small boat. A total of 18 Hotspur Mk Is were produced, 10 by GAl and eight by Slingsby Aircraft.