It is widely reported in the media, that a high proportion of people using public transport choose not to wear a face covering. When challenged many claim to be medically exempt. The current legislation stops short of requiring all passengers to wear a face covering due to medical exemption.
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With seat belt law, a Doctor may issue a Certificate of Exemption from Compulsory Seat Belt Wearing. This certificate must be available for presentation when required to do so by a Police Officer.
The Government should deploy a similar policy for face coverings, to make it a requirement for people to have an exemption certificate which has been issued by an authorised authority (this could be any relevant authority). Anyone not wearing a face covering without such a certificate should be subject to a Covid Fixed Penalty Notice.