Well, he's telling you the exact truth in terms of TLC individual component prices ...Yep I asked him about RCBO and he said nope just RCD, which to be honest for £174 I was a tad disappointed.
1 main switch (£9.10) plus two 63A RCDs (£74.00 total) plus 15 MCBs (£42.00 total) plus an empty 21-way case (£19.60) adds up to £144.70, which with VAT comes to £173.64 - so he was planning to overcharge you by 36p . However, as said, although TLC don't offer them, I'm sure you could find a 21-way MK with all those components already in it for a good deal less that £174.
In contrast, TLC prices for MK RCBOs are £22.70 +VAT (i.e. £27.24) each - so that would soon add up. If you had 15 of those (not that you'd need 15), that would be £408.16 for the RCBOs, but you would save by not needing the two RCDs (£88.80,including VAT).
Kind Regards, John