The Welsh Government has published the advice from their Technical Adisory Group which the Health Minister says 'reinforces the basis for their measures'
Partial quote below
Take home messages
The virus spreads when an infected individual comes into contact with an uninfected individual(s). The likelihood of a contact between an infected individual and an uninfected individual resulting in a transmission is dependent upon the nature of the contact. Some environments and behaviours are more likely to enable the virus to transmit.
Social distancing and quarantining remains highly effective at reducing the risk of infecting others, if observed correctly. Pre-isolating (e.g. not mixing outside of the household) for one incubation period (10 days) would be an effective way of lowering your risk of infecting others. Self-isolation remains of paramount importance for anyone with COVID-19 symptoms.
The best way to protect older family members is not to expose them to potential infection, no matter how well-intended the reason for contact.
Survey data suggests evidence of household-mixing with those outside of the extended household. This is accompanied by a misunderstanding of the risks of transmission associated with mixing. Evidence suggests that increased mixing of households and individuals in indoor settings poses a substantial risk of transmission. Therefore, the fewer households and individuals mix, the lower the risk of transmission, hospitalisation and deaths.
Policy modelling illustrates that keeping Rt1 lower (e.g. by the reduction of social mixing of people generally) would significantly reduce numbers of expected deaths and pressure on the NHS.
Policy modelling suggests that introducing the equivalent of Tier 3 restrictions (e.g. closure of hospitality and entertainment, reduction in mixing) prior to the relaxation of restrictions before Christmas will reduce the number of hospital and ICU beds required for COVID-19 patients, and subsequent deaths.