Prof Neil Ferguson, from Imperial College London, worked on the scientific modelling that the current government advice is based on.
Neil Ferguson's model is based on one particular assumption that can be challenged - that children transmit virus in the same way adults do. This is not consistent with the Chinese data which appears to indicate that the risk of transmission from a child to an adult is in fact much lower.
Of course, the Chinese data needs to be questioned and re-verified but the reality is the outputs from Neil Ferguson's model will vary greatly depending on the input assumptions. I can see why we assumed the worst case scenario for "child to adult" transmission rates (it is safer to be conservative) but this particular input into the model should be scrutinised in much more detail.