- The FTSE 100 turned sharply lower by midday, down 0.35% to 6,711.97 as Covid concerns dominated the agenda with US markets closed for Martin Luther King Day.

The closing of UK travel corridors also saw shares in International Consolidated Airlines top the list of biggest losers on the FTSE, down 2.2% to 158.75p.

Device testing and analytics group Spirent Communications ticked up 0.6% to 264p as its annual revenue rose 4%, helping it to achieve a 'strong' rise in earnings in line with its expectations.

Spirent Communications said it may return excess cash to shareholders, but warned that an ongoing Covid-19 impact on customer spending patterns meant growth in 2021 was expected to be second-half weighted.

Pharmaceutical giants AstraZeneca gained 0.8% to £76.49 on news that it and Daiichi Sankyo had received US approval for their gastric cancer drug.

British gas parent company Centrica fell 2.4% to 49.39p, having announced departure of chief financial officer Johnathan Ford for personal reasons.

Ford was being replaced by Kate Ringrose, who has had been with Centrica for 16 years and most recently was its financial controller.

Healthcare company investor PureTech Health edged up 0.9% to 385p as founded entity and liver cancer focused Vor Biopharma filed a registration statement related to a proposed initial public offering in the US.

The number of shares to be offered and the price range for the offering had not yet been determined.

Animal genetics company Genus firmed 5.4% to £45.46 after it upgraded its guidance on adjusted profit and revenue for the first half of the year, citing a continued strong performance.

Genus's adjusted pre-tax for the six months through December was now expected to be within a range of £47.0 million and £49.0 million, up from £36.6 million a year earlier.

Cosmetics group Warpaint London rallied 10.2% to 92.5p as it, too, upgraded its annual guidance on the back of stronger-than-expected trading in the second half of 2020.

Warpaint London's adjusted profit from operations, including a foreign exchange charge,would exceed £2.2 million, 10% ahead of previously stated guidance of £2 million, on revenue of at least £40 million.

Alternative fuel group Velocys tumbled 27% to 7.51p on announcing that Shell had withdrawn from a joint venture formed to develop sustainable aviation fuel.

Velocys said it would continued to work with British Airways, the other partner in the Altalto joint venture, to secure finance for the Altalto Immingham plant.

Financial product and services company CPP jumped 54% to 505p after it upgraded its core earnings guidance following a stronger-than-expected recovery in India.

CPP's earnings before interest, taxes, depreciation and amortisation for the year through December were expected in a range of £7.1 million to £7.3 million -- 10% ahead of the market consensus of £6.4 million.

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