My right hon. and learned Friend, who is also my constituency neighbour in Buckinghamshire, knows that I have been preoccupied with this for some time. Of course, there is also that principle of UK law called legitimate expectation, which is based on the principles of natural justice and fairness, and seeks to prevent authorities from abusing power, and I think that that is most important.
Essentially, this principle ensures that the rules cannot be changed halfway through the game if an individual had a reasonable expectation that they would continue. Changes to UK law can only happen prospectively—in other words, they can only apply from a point in the future onwards—and cannot be applied to the past. This means that anyone lodging court proceedings can do so knowing that the rules that applied at the time they lodged those proceedings will apply to their case. If that was not so, the law could be retrospectively changed in favour of the state.