There's a huge difference in distributing a vaccine that is unstable above -70 C and one that is stable below -20 C.UK strategy was to go for a range of vaccines with different technologies to spread risk. Pfizer and Moderna are very similar, so it's not unreasonable to choose to prioritise one or the other.
I think Moderna capacity is generally considered less than Pfizer, though the extent to which either can scale as intended is a good one.
The UK vaccine strategy is IMO the only positive of our response as a country, both in terms of protecting our own population but also supporting the wider world through development and funding of oxford, and funding of Covax.
Whether the UK could have secured early delivery, I don't know, hence the rider I made in brackets.
Vaccination is q question of effectiveness and also of logistics,
No point having an atomic bomb if you don't have a missile or an aeroplane capable of delivering it (not a very good analogy perhaps, but I am sure you get the point).