I dont see our capacity in tank tech - where is it? Germany are churning out a Leo2 variant for every country that asks, more armour, slightly longer gun. They have a tank factory. We dont, we would put one together(expensive) for what will be a relatively small number of vehicles. The design/factory costs against such a small number will be punitive. Better to grow NATO compatibility, and face the inevitable facts, that we arent planning a huge tank v tank battle, any time soon.
Chally 2 is fine, but needs a new gun, probably a new turret, new sites, comms etc self defence. The time and cost to develop this, when its already mostly been developed for Leo and M1. I'm taking a pragmatic approach. And, as with F35 better to have 10% of a thousand tanks, than 100% of 100 tanks....
I grant that Boris may feel differently, and want the Vickers Churchill X to be all home grown.