The electrician on holiday is the standard for DIY guys not wanting to admit they are going to DIY so it is always seen as an excuse even if in fact it's true.
Clearly you have the LABC involved and it could be the LABC are issuing a completion certificate or they expect to see a compliance certificate from the electrician? We had a case on here where it cost the home owner an extra £450 because electrics were missed off his application.
With the LABC looking over your shoulder clearly you have to keep to the rules when I did my mother wet room they wanted to know my qualifications before allowing me to submit the installation certificate.
There can be three signatures design, installation and inspection and testing so the LABC inspector could allow you to do some and the electrician to do some but it's up to them no one other than them can say what is being allowed.
Today the LABC can sub contract the testing and inspecting and charge you for the cost. So if the inspector is a sub contractor you can be charged for visit even if there is nothing to test.
Since you only say United Kingdom it could come under many different rules although all parts of the UK follow BS 7671 Wales, England, Scotland and Ulster all have different rules for enforcement although England and Wales both have Part P they are not the same song sheets Wales has far more rules.
There are in wiki the zone rules but some of the rules are seldom followed for example the appendix 12 bit about 2 kW limit for non portable appliance from ring final. It is down to the inspector if an oven can be powered from the ring final and most electricians would be able to argue the point and get their way but as to a true DIY guy then the inspectors word is law.
So to questions in the main we will follow the safe zone routes as any metal protection would need earthing and it would be a nightmare to earth every bit of metal protecting the cable. There is no need for capping be it plastic or metal unless the plaster is likely to affect the cables. The oval conduit is normally used for re-wire as a narrower chase is required and really it is only there to protect from plasters trowel. The plaster likes metal as it does not flex as much but as said earthing is now a problem the oval conduit flexes less than plastic capping so oval conduit or nothing seems best course. You can use Ali-tube cable but hard to buy short lengths so it is rarely used.
The testing is clearly very important
The Emma Shaw case showed that and also of course it does not matter how well an electrician does the job it can be damaged by the plaster so still needs full testing.
I know there are some who will tell you simply don't do it but there are others who will give advice. But you need to be honest and give required information like location.
I would never advise some one with full test equipment to use a FCU rather than extend the ring. However for some one without the equipment required I may well recommend the use of FCU's. Just giving an example how advice changes according to what we think the poster has or does not have both with equipment and knowledge.
P.S. at the moment we still have competent person this goes in June where we drop to just two levels instructed and skilled the higher competent class is combined with skilled. Do remember a competent persons scheme is very different to competent person this is likely why competent person is to be dropped. Now we all need to look after the safety of others.
