Has yartin gone again?
I know from personal experience that a small board is most likely oversubscribed.
I bought a house in 1999 that was rewired in 1994. It has a Hager board with an RCD main switch and not nearly enough breakers for a 5 bed, 3 bath, 2 large reception detached house.
Consequently, some breakers have more than one circuit attached.
I would like to bet that unless his property is a small, unmolested flat, that board will also have more circuits than CPDs.
It should be brought up to date for the sake of the tenants.