As others have said, vaccinated with one dose is not particularly helpful against the current dominant variant.
Apparently we would be able to second dose another 10 million people in the four weeks from June 21st. That is massive in terms of keeping the spread down and hospitalisations low.
I would much rather a four week delay that helps to lower the growth curve sufficiently to avoid lockdowns in the autumn, rather than get back to normal on the 21st and see us back in heavy restrictions in a few months. Those extra second doses really could make all the difference.
Hospitality will certainly struggle with another 4 week delay, but an autumn lockdown would kill many of those businesses off completely.
We don't know what things will be like in 4 weeks. What if things are similar? What if this becomes a seasonal issue every winter?
I don't have the answers to these questions but we cannot constantly just make short term decisions. There has to be a time when we accept we cannot fully eradicate this virus and we have to learn to live with it and mitigate is as best we can.