Found this Radio Rentals sales guarantee upstairs among other documentation.
The date is the 11th of March 1957. As this document relates to an outright sale rather than a rental agreement the customer is getting a very good deal, a two year comprehensive guarantee is truly remarkable for 1957. At that time it was only six months guarantee for cathode ray tube and three months for valves.
The guarantee relates to the sale of a model 392, this begs the question was the set sold under the MRG brand rather than Radio Rentals or RR?
On the reverse side of the document there is a hand written statement indicating that payments finished on the 26th August 1957. So it is evident that the set was sold on a short term credit agreement.