But with Sparky work it seems a bit more complex as none will touch the work and want to quote for a complete project.
A consumer unit is not a single part - it's a collection of parts specific to a particular installation.
Customers buying what they think is suitable rarely works, and it only needs one item to be incorrect or missing and there is a whole load of wasted time while the correct items are obtained.
Even if the exact amount of correct items is provided - what happens if one of them is faulty or it's decided when installing to modify or change one or more of the circuits to something more appropriate?
If the customer has supplied the items, then it's waste more time and money while replacements are obtained.
If the electrician is supplying, they will inevitably have more of the same in their van, so not a problem.
The installation of a new consumer unit involves fully inspecting and testing all of the existing circuits and fixing any problems that are found. That is a majority of the work involved, and customers supplying their own consumer unit changes none of that.
You are also attempting to get 'deals' on Hager RCBOs, which are already some of the cheapest available at about £14 each.