Thanks miechin. The Colobium Sindonis (I am learning to spell it by typing it so much) possibly derives from a tabard and is not a dress as such, because it is worn by a king as well as a queen regnant.

I am on the track of checking if the garment survives from one coronation to the next.

It seems that the very early accounts of this garment were to protect the Supertunica and Imperial Mantle from the oil of the Anointing.

More to follow when I have more reading sorted out and presentable.

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Edit: to refer quickly to the white pleated overgarment the Queen wore to be anointed, I have not yet found an equivalent at an earlier coronation. A king wore a shirt and surcoat, or just a shirt, with both opening at the front with ties.