As far as I understand it, the EU member states are not generally short on doses, more on distribution and other regulatory issues. If they pause AZ, they can use something else which is already being manufactured right now, and likely within the EU, quelle surprise.
I would not be surprised if this is simply a political and economic snub from the EU, one of very many the UK can expect over the coming decades.
The UK has spent the last half decade ENDLESSLY trying to score points against the EU on any and every topic. This sort of wrangling is part and parcel for the relationship the UK has chosen. Basically, if the current UK Government has gone anywhere NEAR this topic, don't expect the truth to linger. This certainly includes the chest-beating around the AZ vaccine, which the government were actually going to require be shipped with a fscking Union Flag on every vial.
Edit: My understanding was based around stories like this suggesting some delays, that AZ were "striving" to deliver, and more dosed being ordered after AZ testing not covering over 65s (at the time), some hesitancy, and general mud slinging. When I say "generally short" I guess I should say that I doubt even the chest-beating Brits will be fully two-dose vaccinated to 80-90% before Autumn. It's been a year and a month or two is second order optimization in my view.
If you are concerned about shortages, there are some other continents to consider first.
https://www.theguardian.com/world/2021/feb/24/astrazeneca-ex...
https://www.biopharma-reporter.com/Article/2021/02/18/EU-add...