I am considering installing a cylinder and boiler in a garage. I may
use two 3 kilowatt immersions. I need to take some cable from the
Consumer Unit to the garage underground. Supplying the boiler,
immersion, lights and sockets in there is more than what a direct
burial 2.5mm cable can provide. Doubling up two of these cables is cost
effective as heavy direct burial cable is expensive. Is it within regs
to have these cables on one 42A mcb at the CU and take it to a garage
CU in the garage and then take all the circuits off the Garage CU?
Makes sense to me.

Or is it best to have each cable on an mcb at the CU and no garage CU
with just two isolators as the cable enters the garage?

Any views?

TIA