Deceptive headline. Zero deaths were reported on that day, because it was a public holiday. The number of people who died on that day is not yet known.
The UK definition is “within 28 days of a positive covid test result”. There was a day in July with no reported deaths, but that used a different definition.
The hospitals my wife works at, in SE London, just about maxed out their capacity before the numbers started receding again. It was close. The ongoing vaccine rollout at the time was a huge morale booster among NHS staff though.
It is too early to say the UK is on top of the pandemic. The delta variant may result in a rising toll despite the mass rollout of vaccines, as the major one they use, the AZ one is only 66% effective. Wait and see, and keep social distancing is all we need to do now.
Eyeballing it from Wikipedia, the 7-day average is probably about 9 or so. That's skewed because we had 15 reported last Monday, which is an outlier from the daily figures over the last few weeks. It's mostly been varying from 3 to 10 since mid May. Hitting zero isn't too surprising looking at the recent trends, but it does look like it might start going up a bit given recent infection rates.