LONDON, July 23 (Reuters) - British plans to roll out daily contact testing within the food chain to prevent workers from having to isolate when "pinged" by the COVID-19 app could cover up to 10,000 people, the environment minister said on Friday. Britain announced the plans late on Thursday after supermarkets and petrol stations struggled to deliver some products due to staff shortages sparked by the pandemic. read more Environment minister George Eustice told Sky News the government had identified 500 key sites within food production that could qualify for self-isolation exemptions. In the week up to July 14, nearly 620,000 people were told to isolate in England and Wales.