- UK stocks opened substantially lower on Friday after trial data indicated a potential treatment for Covid-19 being developed by Gilead Sciences didn't improve patients' conditions.

Local stocks were also hit by the earlier-than-usual release of UK retail sales data, which showed a record 5.1% slump in March.

At 0821, the benchmark FTSE 100 index was off 74.24 points, or 1.3%, at 5.752.37.

Educational services provider and publisher Pearson fell 1.1% to 446.3p on announcing that its revenue fell 5% in the first quarter, owing to disruptions caused by the Covid-19 crisis including school closures.

Pearson, however, also touted ample financial headroom and pressed on with plans to pay its 2019 final dividend.

Luxury fashion house Burberry dropped 3.0% to £13.00 after it said it would keep paying employees' base salaries without tapping UK government support.

Burberry also delayed the release of its annual results by eight days.

House builder Persimmon slipped 1.8% to £21.50, even as it said it would begin a phased restart at construction sites from Monday that had been idled due to the disease pandemic.

Pharma giant AstraZeneca was broadly flat at £81.84, having released further positive results from a clinical trial of a drug used to treat prostate cancer.

Trading platform IG rose 1.7% to 748.5p, as it reiterated its intention to pay a dividend amid a jump in trading activity owing to market volatility created by the Covid-19 crisis.

IG, however, also said its costs would be higher than expected as it invested in its business.

Component manufacturer for the aerospace and defence sectors Senior gained 1.0% to 61.45p on announcing that it had decided to hold onto its aerostructures business, having invited bids last December.

Senior also said it had furloughed around 17% of its workforce as the Covid-19 crisis crimped customer demand.

Immunotherapy developer Scancell soared 73% to 8.8p on announcing that it had initiated a research programme to develop a vaccine for Covid-19.

Cybersecurity group Shearwater dropped 9.3% to 263p as it launched a share placing to raise at least £2.5m to fund 'considerable growth opportunities within its markets'.

Pesticides company Plant Health Care fell 4.4% to 6p on posting a full-year loss, as its sales fell and margins were squeezed by US trade tariffs imposed on China.

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