Ok, so if i do away with all spurring here and continue the ring circuit from the socket in the house > to the shed > to the sockets and switches for lights (which will all be FCU's) for the decking > back to the remaining sockets in the house > before ending back at the CU. If you understand what i mean. Put everything on the ring.
Would that be acceptable?
Skamuk
You really do need to know what you are doing with a circuit before you start planning things. You need to be able to calculate the requirements for the circuits, whether the volt drop exceeds the maximum allowable, whether your accessories are rated for the potential fault current and so on and so forth. I commend your enthusiasm but I cannot commend your level of understanding of electrical installation.
As you have a friend who is prepared to risk their career to sign off your work for you then the best bet would be to ask him what you need to install.
You are aware that by law all electrical power installations across a garden need to be notified to building control or self assessed through a competent persons scheme.
The key points are to design a circuit within the wiring regulations and the building regulations. You should know what these regulations are before deigning a circuit. BS7671 the wiring regulation and the on site guide and the electricians guide to the wiring regulations and approved Document P would assist you to understand the requirements.
You need to differentiate between lighting circuits and socket circuits by fusing them appropriately.
You need to ensure that there is no possibility that cables can be overloaded and overheat (which is where spurs on spurs are not allowed) by using the appropriately sized cable for the design current and protective device.
A ring final circuit using 2.5mm² cable and a 32A mcb should not exceed 100m².
Light switches are rated in general to a 10A maximum load and a lighting circuit should take this into account.
Your hope of extending the ring out into the garden can be done but it would require some interestingly inconvenient rewiring in the house especially if you are using SWA.
The use of multiple FCUs for your lighting circuit seems overkill and seems to indicate that you are not sure how you should do this.
I hope that this gives some useful information but also provides some warnings that maybe you need more information to be able to install this in accordance with the regulations.