My renewal quote with ERS through Gott and Wynne was £840 last week including pan-European breakdown cover. LV quoted £440, so that was that. G+W are excellent, but there is only so much that they can do.
Did you have to phone LV? I just tried their online quote system and they don't list either the M3W or the Super3...
Last time I asked LV (good insurer) they had no record of a car called a Morgan 3 wheeler on their systems. I laughed just now to see their online configurer allows for a Morgan F for dates up to 1952, then 2020 on

so clearly their underwriters are assuming the Super 3 is the new F type (impressive deduction!). They do have vintage types like Austin 7s on their configurator so a bit bizarre...