I have a 2-wire overhead sub-main to a large shed 40-45m away. The house
earthing is TN-C-S (with an earth rod, ref other append) and the shed
earth comes from a local earth rod; there's an RCD in the shed CU. I
plan to replace the overhead feed with 3 core SWA in the ground (0.5m
deep, with warning tape above it at 0.3m deep), terminating the SWA
internally in IP65 adaptable boxes at each end and running the final
couple of metres in T&E.

The feed will come from a non-RCD protected MCB in the house CU. From
the TLC cable size calculator it seems that buried 2.5 SWA is OK up to
about 3.6kW for non-lighting circuits (about 2.2kW for lighting
circuits). I plan to either feed the SWA from a 16A MCB in the house and
to use a 10A MCB in the shed or or to use a 16A type C MCB in the house
and a 16A type B MCB at the shed. Any comments?

I believe the correct earthing in this situation is to export the house
earth down the SWA (hence 3-core, the armour will only be earthed at the
house end) and to remove the shed earth rod. Once again, have I missed
anything?