Comment by Meon Valley Records:
1953 also fits with the tax code printed on the label.
1948-04-09 DT(48) Purchase Tax increase 66.6% CT on Decca
1950-12-30 DTP Price increase CT+IP on Decca (AT stamps)
1953-04-15 N Purchase Tax reduction 50% (NT on stamps)
1955-10-27 RT Purchase Tax increase 60%