I managed to source a Cob size kicking strap.
Made by Ideal Equestrian in black Euro Tech
Discourages the cob from bucking while carriage driving, prevents the ability to put a leg over the shafts or kick the driver.
Attaches via the crupper & then each side of the shafts (not quick release), it has plenty of adjustment on both sides. (See 2nd photo)
Shortest length 168cm x 2cm wide
Longest Length 178cm x 2cm wide