The most extraordinary sound I heard with MBL 101 driven by Joule-Electra VZN-300. I am sure that '121" ia a bit easier to srive.
if you don;t want to deal with OTL amplifier's heat then second best, IMO, is the pair of Spectron Musician III monoblocks. Much better then JC-1 (as per reviewers) and less expensive too.
Plus, as you live in England, Musician III is a modular amp and if something going wrong you ship plug-in module(s) by air and in a few days get them back repaired, plug them into amplifier and enjoy the music again. Moreover, they increased warranty to 7 yrs I believe.
Finally, BAT VK600SE-M, Plinius Reference and Pass Labs XA 200.5 will drive these speakers very well too but $$$