There is a bit more back ground. This is a click bait story which has caused a lot of distress and worry. I have seen the clickbait story and I think the source is an online insurance comparison forum but I won’t pretend to have spent hours tracking it back.
Here is what the Association of British Insurers say at https://www.abi.org.uk/products-and-issues/topics-and-issues/coronavirus-hub/motor-insurance/
“Your cover will not be affected if you drive during the lockdown period. However, all motorists should follow Government advice and avoid non-essential travel.”
The first sentence is an accurate statement of the law and the second sentence is wise advice but not law.
Insurers do not have magic powers to invalidate insurance on a whim. If you have paid your premium you are insured. If there is an innocent explanation for this click bait nonsense it is a conflation of travel insurers not paying out if you have flown overseas contrary to Government advice. Those Government advice clauses are specific to every travel policy I have seen but not road traffic risk (ie vehicle) policies.
However, I go with the click bait basis and I do not think there is an innocent explanation. To void a policy or to avoid a payout the insurers will have to show you breached your duties under the Consumer Insurance (Disclosure and Representations) Act 2012. I summarise the basic thrust of the Act as “unless your insurer asks you a question which you answer recklessly or dishonestly then you are covered” and this false information is not coming from the insurance industry.
The official Pdf for the Act is here. https://www.legislation.gov.uk/ukpga/2012/6/pdfs/ukpga_20120006_en.pdf
So, if you want to use your vehicle during lockdown you are insured. As this is not a matter of local regulation the law applies across England and Wales.