Ryzen, I have a life thank you. i'm grateful that you've enlightened us all with your qualifications. Me, I've also got a few years under my belt in these matters including advising NICEIC on specialist installations and earthing , lecturing in electrical installation and practice, a senate member of the IET and a few others I won't bore you with. My knowledge could reasonably also be taken as OK.
I cited Screwfix as it's a pretty comprehensive catalogue that porkchop could read to give him some guidance. The catalogue can readily be picked up in most major towns at Screwfix stores or ordered online if he so wished. He doesn't need a trade account to purchase and they'd be slightly cheaper than the DIY sheds. I could just as easily have recommended Toolstation.
Porkchop doesnt need the technical stuff available in CEF or Ednundson catalogues that contractors like you use and besides could not purchase one from them anyway. Even you should agree with this.
Demanding discounts does NOT mean that you pass on these savings to the customer. At the end of the day, if pushed, you will tell the customer the trade cost of the consumer unit. The customer has no means of establishing the veracity of the figure you give. You may be honest about the figure, but not all contractors are.
Your post says that you will replace faulty equipment. Is that equipment purchased by you or the client? Your earlier answer seems to contradict this.
I don't doubt you are part of a nationwide company but lets get real here. £400 quid for doing the job porkchop wants all in including a new consumer unit? No sign of you trying to reassure us that you could do it for that price. Clearly, your not handling the financial aspects of your installations.
Incidentally, my favourite bedtime reading are the CEF and Newey and Eyre catalogues. That way my company can provide an honest cost of an installation rather than increasing the equipment cost to slightly decrease the labour cost.