LONDON (Reuters) - Britain will launch a COVID-19 mass testing pilot scheme in Liverpool this week, offering everyone in the city tests whether or not they have symptoms, in an attempt to find a better way to use testing to limit the spread of the coronavirus.Prime Minister Boris Johnson had promised a “world-beating” national test-and-trace system earlier this year, but the scheme has disappointed and the government’s scientific advisory body said last month its impact on virus transmission was marginal. The United Kingdom has the highest COVID-19 death toll in Europe, and a second national lockdown is due to come into force in England on Thursday. The government said the Liverpool pilot would start on Friday using PCR swab tests, the default testing method to date, as well as new lateral flow tests aimed at delivering faster results without the need for laboratory processing.