ARW wrote:

When I went to the ElexShow this year the CU manufactures were all
showing of their new CUs (obviously not MK) with SPDs built in at the
head end next to the main switch.

Yes, from looking at them there, and from various youtube sparky
channels, the SPD seems to be wired between the L & N output sides of
the main switch and earth ... not seen one in a CU connected to L via a
32A MCN as the leaflet shows.

The other option apart from putting them in the CU, is to put them in an
separate isolator switch, e.g Wylex REC2SPD, Fusebox F1M2SPD, Lewden
SRG1VCU-RM

https://www.tlc-direct.co.uk/Products/WYREC2SPD.html

https://www.gil-lec.co.uk/fusebox-f1m2spd-inline-surge-protection-unit-with-100a-main-switch

https://www.medlocks.co.uk/lewden-retrofit-type-2-surge-protection-unit-32a-mcb-100a-2p-main-switch

The last one *does* seem to include a 32A MCB to connect the SPD to.