The modern form of caution is:

Research (Shepherd, Mortimer and Mobasheri (1995)) established that, on a statistically generous assumption, the entire caution, when read through once is understood by only 14% of the general population. Since suspects tend to be less well educated, the proportion of suspects understanding it will be rather less.

If most people do not understand the caution. What does it mean, then? I prefer to explain it backwards.

1. What you say in this interview will be used in court.
2. If you are charged and plead not guilty, then the court can ask whether anything you say in court could have been said now. If you mention something new in court, the court may be reluctant to believe it.
3. You do not have to say anything. The prosecution must provide all the elements of it's case itself, and you have no obligation to take part to help them.

Any interpretation which can be understood will not do justice to the rules, since these themselves are understood properly only by a few senior judges.