"John Rumm" wrote

They will generally all be able to take the double width RCBOs. Only the
taller ones will take the single module ones.

That does suppose that you can still get any spares that fit. A good
number are interchangeable, although technically speaking mixing brands
would void the type approval.

Thanks John - can you clarify please
I can't afford to lose breakers, so double width ones are non-starter.
How do I know whether my box is a "taller one"

Not sure what you mean about voiding type approval.
What difference does the manufacturer of each individual MCB or RCBO make?

TIA

Phil