It's much more likely to have peaked because of Euro finals on 11th July and school holidays starting on 15th July
It should take about a week to start seeing the effect of a change in policy. From incubation time to testing to results. Usually, we count two weeks to be sure.
It could be coincidence but this date was planned and intentional.
I could reframe your hypothesis in a falsifiable way such as "perhaps ending lockdowns in the UK caused individuals to spend more time outdoors or in open air restaurants rather than smaller closed doors activities such as dinner parties", or "perhaps ending lockdowns in the UK caused people to spend more time in other locations rather than large shared ventilation apartment complexes".
From this article:
> “Something strange is happening in Britain,” the Washington Post declared this week. “COVID cases are plummeting instead of soaring.” A few weeks ago, when the country’s new daily-case total was around 60,000, the prominent British epidemiologist and government adviser Neil Ferguson declared that a rise to 100,000 a day was inevitable, and that 200,000 a day was possible. The country is now at 27,000 and falling.
https://assets.publishing.service.gov.uk/government/uploads/...
That's showing hospitalisations rather than cases, and most scenarios show the peak in early August. Hospitalisations lag cases, and it looks like early August will be right: we haven't seen the peak yet.
Peak was several days ago.