I am planning to add a spur to my kitchen circuit so I can have access
to power outdoors. I have identified all the sockets that are on the
circuit I want to add my outdoor spur. I have checked the sockets at
the end of the circuit to determine whether the circuit was a radial
or ring.

It is a radial. If it is the only circuit in the kitchen, it is grossly
underpowered. It will just run a couple of appliances. For a large kitchen,
it is a definite no. You may have:

Washing machine 3kW
Tumble Dryer 3kW
Dishwasher 2kW
Kettle 2kW
Fan oven 3kW
Toaster 2kW
Microwave 1.5kW

on the circuit, amongst other things. If all going at once, it will draw
close on 70A. OK, this is unlikely to happen to practice, but 20A is nowhere
near enough. I certainly wouldn't want to draw more off it.

If you have a utility room with the washing machine and tumble dryer off a
separate circuit and the oven is off the cooker circuit, it may be enough,
though.

My guess is that the circuit is a radial, as rings are usually "fused" at
30/32A. It is obviously only a guess. You can get a better idea by measuring
continuity between the two end conductors, which will be low for a ring main
(hopefully) and infinite for a radial (hopefully).

So, in summary, I wouldn't dream of taking more spurs off this circuit. Your
kitchen may need a rewire if it is of any size and only has this circuit
feeding it. Your outside electrics should really go back to its own RCBO on
the consumer unit (non RCD side if you have a split). Alternatively, you can
use an MCB on the RCD side, but this will probably lead to nuisance trips.

Christian.