This is exactly what I predicted would happen a few weeks ago when the announcement about under 30s was made.
IMO it's unethical to require anyone to accept AZ when Covid infection rates are so low, and there are available alternatives that are just as effective, if not more effective. But because the government has bought lots of doses of AZ, and politically they want to meet their target for offering all adults a vaccine by a certain date, they pushed ahead and through the timing of this announcement have effectively forced 40-50 year olds to accept AZ.
It was quite different back in January when infection rates were sky high and there was limited vaccine availability. In that situation it was right to offer AZ, particularly to people at high risk from Covid.
I'm 41 and had my Pfizer vaccine yesterday. I'm grateful to the other posters who shared information about which centres were doing which vaccine - without that info I would certainly have ended up having AZ. The vaccine centre I went to was super busy and the vaccinator said it was because so many people were refusing AZ.
At this point they should just offer everyone a choice, that would be better than having loads of people refuse vaccination entirely.