BTW - I will be protecting the outdoor socket by using a RCD adapter
and burying the cable in PVC conduit 45cm+ under ground.

Ensure you use SWA armoured cable for this. It isn't that expensive and is
much more suitable for burial than T&E.

Do you think my best bet would be to spur of the 30 amp ring or
install a new consumer unit either with more MCB's or in addition to
my current CU?

Obviously, a new consumer unit would be best. However, a 13A/30mA RCD fused
spur on the 30A ring would suffice for now.

Christian.