"Cannot afford a credible force...? What does he mean by 'credible' and why can we not afford it?"
have you missed all the economic projections WEBF? We're in deep hole - something has to give. Quite a few commentators see the Army as being the major beneficiary of any increase/alignment of spending because that's what they see is needed in Europe. They see that carriers (or even navies) are irrelevant on the ground in Ukraine and it's another Ukraine that worries them most.
As for Hastings - I feel he's pretty full of his self -importance but he is read and recognised by a very large number of people. He has influence - doesn't matter if you like it or not. And someone is feeding him a story for sure. My concern is that we'll get another exercise in stretching the UK's armed forces thinner and thinner again without anyone doing something about investment (which desperately needs to increase) and a cut in some missions - we can't continue to do everything we currently claim to do