They surely must have that data. We get a breakdown every day re community vs HCW cases. 1 in 4 of our total cases is an HCW.
They've got some data like that but what's been released of it is limited.
They've started doing mass test samples and using the figures to compare. I think it becomes easier to do stuff like this as cases go down as it frees up resouraces to do sample testing and monitering. It's already clear health or care workers are much more likely to be affected. I also think there'll be a bucket load of data that isn't made public because it'll just fuel bickering when difficult decisions get made.
I also from working in government can pretty much guarantee they'll have an absolute endless amount of data about how many people are likely to follow advice, behavioral patterns, people per area, and so forth. They'll be looking really closely at data from other countries who are doing things differently or on a different timeline. So they'll know full well what is likely to happen when they tell people they can go sit in a park, etc.
I really don't see how more people being out will make any significant difference, personally. The people ignoring social distancing will be the same ones who already were ignoring it. People have also still had to go out to do shopping the whole time, and this involves queuing together, bumping into each other, being in a large building with circulating air with hundreds of other people and touching all of the same things as them. If something like that has no noticable impact on case numbers, a load of people sitting or walking about not particularly near each other in the open air is a near non event.
Public transport would be the head scratcher I think. All well and good telling people not to use it, but where I am for example, 100% of people who commute into London have no choice, and it's not possible to run more trains than they already do during peak times. If the aim is going to switch to eliminating the virus rather then just getting numbers under control this seems like a pretty massive obstacle. Probably a bigger one even than hospitality venues, where you can at least regulate distance and capacity to a degree. Though I don't think eliminating it is ever going to be an option in England anyway.