Secondary school open days/tours

I can't find in the govt guidance whether secondary schools are allowed to hold open days/tours for prospective parents? Some of the schools around here are saying they are not allowed to within the current guidance yet my ds's school is holding 4 open mornings over the next fortnight. I am wondering whether they are being too relaxed about things especially as they don't have anything in place like separate areas for year groups inside/outside, nor staggered lunches/starts/finishes etc and are carrying on with putting pupils in various different classes of children even though they never set for ability anyway. Many thanks for any clarification on the open morning situation.