Only people who have tested positive for coronavirus and subsequently have died are counted in the deaths. But only people admitted to hospital are tested. Therefore there may be community deaths not counted.
As the govs own website says
As of 9am on 28 March 2020, a total of 120,776 people have been tested, of which 103,687 were confirmed negative and 17,089 were confirmed positive.
As of 5pm on 27 March 2020, 1,019 patients in the UK who tested positive for coronavirus (COVID-19) have died.
The figures for test results and for deaths are compiled from different sources. This is why the figures for deaths are reported from an earlier point in time than the figures for test results.