The Futility of Partial Quarantine?

It seems, at times, that the UK can get anything wrong is its attempts to curtail the Covid-19 pandemic! I entirely agree with Gabriel Scally (Bristol University and Independent SAGE), that the new 'toughened' regulations for International travel are a fiasco (https://www.theguardian.com/world/commentisfree/2021/jan/28/uk-covid-travel-quarantine-hotel). As Scally notes there is no such thing as 'partial quarantine'. The new regulations are said to require travellers, coming from 22 'high risk countries', to isolate on arrival in the UK. This is at their own expense, in airport hotels (that's a recipe for avoidance and other inappropriate behaviours). Another major difficulty with this requirement, is that where someone started from, doesn't give you the whole story about risk. Passengers change planes and they often sit in airport lounges, for extended periods, with people from all over the globe. Even worse, some 60 occupations or groups will be potentially exempt from the isolation requirement. This even includes some people who commute Internationally on a weekly basis (repeated trips must increase the risk of carrying the virus). Exemptions, also make it less likely that others will stick firmly to the rules. The UK borders seem excessively porous for Covid-19, in all its varieties.