LeMieux CONTOURED BROWN GIRTH SLEEVE COVER, size L (75 cm, 30"), NEVER USED, with 2 elastic outer straps and 2 inner velcro opening straps for ease of attaching to the girth.
LeMieux sell them for £35, asking £20.
Collect from Minstead SO43 7GL or can post at cost.

From their website:
The LeMieux Simuwool Dressage Girth Cover is a luxurious and breathable half-lined cover that provides the perfect blend of comfort and sophistication.
Half-lined with super soft high density faux lambswool, this luxurious LeMieux Simuwool Dressage Girth Cover is breathable with just the right amount of cushioning to prevent sweat build-up and rubbing.
The rolled edge prevents the girth from coming directly into contact with the skin, maximising your horse's comfort whenever you're in the saddle. The faux lambswool is particularly ideal for sensitive skinned horses who struggle with rougher-feeling fabrics.