"Apparently the UK no longer has the capability to build highly complex and technologically challenging military equipment like this anymore"
They do, but nobody wants to build such equipment in the UK. BAE Systems is the main company that produces mine-protected vehicles, but they are mostly made in South Africa and obviously weren't considered suitable compared to the Ridgback or the Mastiff. Even Pinzgauer (which BAE Systems recently acquired) has or is due to shut down in the UK now with production shifted to South Africa. And any production facilities are going to move to FRES construction, support and upgrades once that comes into service. Leaves smaller companies like Jankel Armoured Engineering and NP Aerospace to "uparmour" and "weaponise" stuff the UK has bought in elsewhere.