Swindon Local Studies Collection has an image of the commemorative booklet containing an illustrated history of Swindon works in Persian which was produced when King Amanullah visited the Great Western Railway‘s works on 21 March 1928.
The Queen did not attend as had been planned: “it was understood that the Royal lady was too fatigued to bear the journey” reported Railway Gazette on 23 March 1928.
The booklet included portraits of the GWR’s Chairman, Deputy Chairman, General Manager and Chief Mechanical Engineer.
British Pathe has some old film KING AMANULLAH IN SWINDON:
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Royalty. Amir of Afghanistan Amanullah Khan visits England. The Amir and his entourage visit a railroad engine factory. Dark but interesting footage. The group watches a worker using a gun to spray paint or some sealant on a railroad freight car; the man wears a mask to protect himself from chemicals. The men walk by a locomotive rotating on a turntable outside factory. Interior: they walk through large space w/ many sets of train wheels lined up. Heavy machinery moving another set of wheels overhead. Next; they gather around a finished locomotive. Exterior again;the group walking along beside train. Entering train coach. This visit is probably from 1921 [sic]; when A.K. signed a treaty w/ Great Britain.
I suspect 1921 should say 1928, making it the same as the visit above and as listed by the British Film Institute.
There is also a photo The King of Afghanistan visits the Swindon railway works, Wiltshire, 1928 at the Science & Society Picture Library.