I think this is a poor judgement.
Johnson looks like he is relying on the possibility that the deadliness of the virus is weakening in the summertime, in the same way as the flu.
That's presumably because the numbers of deaths from covid-19 have declined faster than the number of new cases in the UK.
It may prove true that the virus will weaken. But that's one helluva gamble with people's lives. And risks an economy-depressing second wave.
Another week or two of full lockdown would have put the UK in a much stronger position, in my opinion.