I doubt he will shut the country down the UK has no where near as many cases as Italy, Germany or France yet. Really any measures before that should be stopping flights into the country from Italy etc having the elderly and vulnerable self isolate. If you impose it now it's far too early 590, 29,764 people have been tested of those 590 have been found to be infected that's only 2% (1.98%) of those tested, so far 10 people who were in the high risk categories with underlying health conditions have passed away that's 1.7% (1.69%) of those infected. So far globally of the closed cases 73,423, 94% have fully recovered 6% have passed away of number still infected 56,352 90% are mild condition and 10% are serious conditions. Globally of the the 129,775 who are or have been infected 4,751 people have passed away 3.7%, 0.3% above the rate WHO originally stated of 3.4%, but in the UK that rate is only 1.7% and 100% of those were in the high risk categories. Swine flu infected 28,500 killing 337 in the UK 67% (226) were high risk 33% (111) had mild or no pre-existing conditions a death rate of 1.18%.
They expect this to peak end of April start of May. So no point locking down now as people will start to ignore it when it will be needed most.