LONDON—As the United Kingdom’s COVID-19 death toll approaches 100,000, grief-stricken relatives of the dead expressed anger at Prime Minister Boris Johnson’s handling of the worst public health crisis in a century. When the novel coronavirus, which first emerged in China in 2019, slid silently across the United Kingdom in March, Johnson initially said he was confident it could be sent packing in weeks. But 98,531 deaths later, the United Kingdom has the world’s fifth worst official death toll—more than its civilian toll in World War Two and twice the number killed in the 1940-41 Blitz bombing campaign, although the total population was lower then. Behind the numbers there is grief and anger. Jamie Brown’s 65-year-old father died at the end of March after it was suspected he contracted COVID-19 while traveling on a train into London for work. At the time, the government was mulling a lockdown. Told by medics …