Many thanks to all those who took the time to reply and the interesting
debates that ensued.
I have found the manual for the slot in cooker with ceramic hob that has
just been removed. This unit was rated at 11.1 kW and has been running quite
happily on a 32A MCB and 6mm T&E cable for the last 6 years or so.
So with the comments received by all you good folk and the above facts in
mind.... I am going to go for 32A MCB with 6mm T&E from the CU to the DP
Isolator then 4mm T&E from the DP via connection unit to the two appliances
(oven and hob) both rated at 5.18kW and 5.4kW respectively (10.6kW total).
The manual for both the oven and hob state that they can be wired with 4mm
that is unless someone tells me different before the weekend....deadline
from the boss to get them working :-)
Many thanks once more