UK elders are not specifically required to destroy or keep anything by law.
Any data they keep has to comply to the Data Protection Act about how it is obtained, for what purpose and how long it is kept for. An individual can make an information request at any time to see the data held about them The recent audit letter and the letter posed by WiFiBandit above demonstrate that the WTS is very prescriptive in ensuring the minimum data is kept, for (I repeat) two key reasons:
1 - to prevent elders keeping data that either does not comply with the DPA or data that could be used in a civil case by someone wishing to bring a case against a congregation on the basis of information held about them.
2 - to keep to a minimum data that could be used by the authorities against the organisation.
Point 1 is because elders are often idiots and careless about what they write down and keep hold of.
Point 2 is because the WTS has a persecution complex and imagines they are going to be oppressed at some point.
It's a matter of opinion but asking elders to audit their records against the published benchmarks is, in my view, not quite the same as getting them to destroy evidence or cover things up. If they have no legal obligation to hold the data then they cannot be accused of destroying evidence. When it comes to child abuse the processes are clear about what should be held. This is so some measure of "due diligence" and "duty of care" can be demonstrated rather than adherence to any legal obligation is concerned.
They can, however, be asked to explain how such instructions really tally with an open, transparent and progressive organisation, especially when it comes to child abuse. The instructions can be compared with other organisations to illustrate the predictably huge gap between the WTS' claims of being leaders in child abuse management and the reality of what is best practice in the vast majority of similar organisations.