Sadly, no matter which way you look at this, the bust is wrong.
The British Army stopped its staff officers (GSOs) wearing staff gorgets after the Great War (Where the distinction became to be viewed as toxic and counter to the cohesion of the Army). Thereafter and since, the staff gorget has been a badge of rank, worn by full colonels and above.
The gorget is most often crimson, but there are some regimental variations. For colonels and brigadiers (Which stopped being 'generals' in the British Army after the Great War) the cords are the same colour as the gorget; for major generals and above the cords are gold. In short, lieutenant colonels in the British Army have not worn staff gorgets since the Great War.
The bust could be corrected either by removing the gorget or adding one or more pips to make the figure a full colonel or a brigadier. If the latter then you would also need to alter the cap-badge, since full colonels and brigadiers wear the staff cap-badge and generals the generals' cap-badge.
Johnny Frost was captured at Arnhem and it a a sad if understandable rule under the Military Secretariat that an officer cannot be promoted while in captivity. Frost was liberated in March 1945, and after the war commanded the Airborne Division's battle school, before returning to command 2 PARA during the Palestine emergency - still as an acting lieutenant colonel. He attended staff college, completed a tour as a GSO2 (Major) in Scotland before promoting to substantive lieutenant colonel and being assigned as GSO1 with a Gurkha brigade in Malaya. He wasn't promoted to full colonel until 1955, when he commanded the Infantry Support Weapons Wing, and to brigadier in 1957 when he assumed command of 44th Parachute Brigade. He was promoted only once more, to Major General, commanding the 52nd Division.
Interestingly, and in my view, the bust shows a far closer likeness to 'Shan' Hackett, who commanded the 4th Parachute Brigade at Arnhem. Like Frost he was captured, but unlike Frost he was seriously wounded. One German doctor believed his wounds to be terminal and sought to administer a lethal dose of morphia to relieve his misery, while another believed he could be saved - in one of those odd twists of fortune, the second doctor prevailed and, largely due to the serious nature of his wounds and the apparent lack of need to guard him, Hackett was able to escape with the help of the Dutch underground. A superbly courageous family, the de Nooijis, helped him until the underground were able to assist him in making his way back to England.