There is a difference between how long are you required by statute to keep records and how long is it in your interests to keep records. To take the tax angle as an example (and it is not the only angle), there is a statury requirement to keep them for a set number of years (6 or 7, I forget, depends where you measure from) and destruction within that period is an offense, regardless of the benefits of retaining them. Once that period has expired, you no longer have (for tax purposes) a statutory obligation to retain the records. HOWEVER, in certain limited circumstances HMRC may have the power to enquire into those years and, if dissatisfied, raise discovery assessments. Were they to go down that route, the burden of proof tends to rest with the taxpayer, which burden is obviously harder to discharge if the records are destroyed.