This trader advert from February 1951 displays a whole range of mains powered battery eliminators.  From the beginning of electrification in the UK various companies offered such boxes which converted your mains supply into suitable multiple voltages to save buying expensive batteries.  However, in 1951, these were not cheap.

A Convette for every type of Battery Set!

(From  left to right, top to bottom)

DB3 for practically every standard all-dry Portable. £4. 2. 6.
VPA for Vidor Attache, Pye P31BQ and Philco B2601. £3. 19. 6.
M2V replaces both HT batteries and 2V accumulator in all sets. £6. 16. 6.
BC1 for Bush BP10, Cossor 499 Portables, using batteries No.4 and B104 or equivalents. £4. 2. 6.
PR1 for Personal Sets using B114 batteries or equivalent.

From your usual wholesaler.
Any Battery Set a Mains Set too!