Chris B wrote:

Having just read this I quite agree its got nothing to do with
efficiency as any sane engineer would define it.

https://www.electricradiatorsdirect....ctric-heating/

most electric heaters will begin with a base rating of 30%

It gets less sane if you read

https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32015R1188&from=EN

because the base rating turns out to be 40% (100/2.5) not 30%