Jack Lawson wrote:

Tim+ wrote:

Is it definitely a RCD tripping and not just a MCB?

it is in fact a MK (ELECTRIC) 5916S Thermal Magnetic Circuit
Breaker, SENTRY Series, 240 VAC, 16 A, 1 Pole, DIN Rail

Many thanks - problem solved.

Well, mystery solved but problem remains. What else is on the MCB that
trips? Is the circuit wired with 2.5mm^2 cable? It may be possible to
replace it with a 20A one, or a "type C" 16A one.