The UK is starting from the assumption that the majority of the population will get infected, no matter what precautions are taken, so it's better to manage how

The UK is starting from the assumption that the majority of the population will get infected, no matter what precautions are taken, so it's better to manage how we get there starting now rather than delaying the inevitable (quarantines will have to end at some point, after which re-infection of the population seems likely anyway).