The Met Office guidance states that when a Red Warning is in effect, 'you should avoid travelling, where possible, and follow the advice of the emergency services and local authorities', which suggests that travel is not banned but should be made with caution. What may have a greater impact is if travel has been prohibited by the local authorities or police in a specific area - it is important to note the difference between 'should not' and 'must not' when guidance is provided by the authorities.