The huge gas leak in the North Sea that has now shut down three platforms could take six months to seal.
Gas has been leaking from one of the platforms - owned by Total - since Sunday.
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Among the first to receive the tests will be critical care nurses, intensive care staff, ambulance workers and GPs.
The supercentenarian from Alton, Hampshire, who lived through the Spanish flu, is under Covid-19 lockdown.
Mr Johnson, who has a "temperature and persistent cough", says thanks to the "wizardry of modern technology" he can continue to work.