The latest "big change" in coronavirus infections across the UK is of "great concern", England's deputy chief medical officer has warned.
Prof Jonathan Van Tam said people have "relaxed too much" over the summer and "we have got to start taking this very seriously again".
If not, the UK will have "a bumpy ride over the next few months", he warned.
He said that infections among younger people in EU countries had later filtered through to older age groups.