The only possible reason for a lockdown (shops and restaurants closing) would be a new vaccine escaping variant that would kill hundreds of thousands of elderly and infirm people.

With the existing variants endemic in the UK and the effectiveness of vaccines there is no justification for a lockdown (in any country, in my opinion) - there is however some justification for non pharmaceutical interventions such as masks, social distancing and contact restrictions to reduce the infection rate (R) without restricting quality of life until everyone who wants a vaccine has had both shots.