To be honest, MY ideal solution would be to simply gift a brigades-worth, 150 or so, challenger 2 tanks to Ukraine. We dont need them as we have such low numbers planned for challenger 3 that in any real full-scale war they would simply cause integration and supply issues when mixed in with all the hundreds and thousands of Leopards and Abrahams. In any all-out war, our role is no longer to hold the fulda gap against the warsaw pact forces (many of whom are now in NATO now anyway) until the American cavalry can arrive but to support Norway and The Baltics with lighter forces. Germany should be able to defend itself. Aborting the upgrade to C3 would save... a few hundred millions at least which could be used to beef up other aspects of our defence portfolio, such as submarine and anti-submarine warfare, our air forces, and nuclear deterrant.
A few dozen tanks were all that were sent to Afghanistan I believe - not in an armoured warfare role but simply to patrol while being almost immune to IEDs. We could still do that with our remnant few dozen which could also be a cadre for any future expansion. It would lead us unable to join in any land expeditionary force, like gulf wars I and II, but at least in the latter case I see that as a plus. The only thing I forsee in the medium term is a defence of Taiwan, and we dont want to be going anywhere near there with land forces (or the white elephant carriers which wont last more than a week).
Historically, the only reason for us making our own tanks was for expertise and sales purposes, but since we have closed and sold off our capability for that, and BAE is basically a US company now (bigger US ownership than British anyway) why bother? The only other nation we have a land border with is Ireland... and they dont have any tanks either.
Just my two penn'orth.
PS. Slightly off-topic... but the most un-PC real unit badge ever?:
Air force medic patch