I think that is a slightly different issue (without having seen the speech).
So there is this idea of opening up in the summer because otherwise it would be autumn or winter and there would be flu, RSV etc. Flu and covid together are thought to be more lethal.
However, it depends a bit on how you open up.
Before July 19th we had very few restrictions in many respects, anyway.
Allowing people to have weddings and birthday parties, especially when they can do this outdoors in the summer has some point to it.
However, masks remain a good idea indoors, and Whitty famously said he'll continue to wear them.
So I don't think he was suggesting a free for all so that we all have a sort of chickenpox party for covid over the summer.
Rather that if we are going to ease restrictions for a portion of time, summer is better to do this rather than winter.
Whiity has also said that winter is likely to be difficult, and Boris is no longer talking about irreversible easing of restrictions and you can of course make of that what you may.
I think if we are careful over the summer we will be better placed for the difficult autumn and winter.
From what I have seen the scientists were agreeing with that.