I need full bore, though, really. The entire house, hot and cold is mains
pressure. I'd prefer to do the pipework in flowed 22mm pipe.

I'm thinking something like screwfix item 52117.

Nah. I'm running the entire house's water supply through it. Screwfix 52117
wouldn't have remotely enough flow rate through it. The 19mm bore one
someone else suggested is actually quite tempting given that it is
presumably inside diameter and so is really not far off that of 22mm copper.
However, a smooth bored flowed bend 22mm copper setup seems more reliable to
my mind.

Christian.