Re-posting this, as I think it is Arthur as the uncredited guard on the left in a THE ADVENTURES OF ROBIN HOOD episode from 1957, "Brother Battle". The brother is Francis de Wolff.
Not only does the guard on the left look like Arthur Lowe, the one on the right bears a strong resemblance to Clive Dunn!
Now if only those arrows on the shield in the background would start snaking around and retreating...