Retaining records for Tax - as legal obligation

The general rule of thumb is 6 years to retain documents for business. There are exceptions:
If an enquiry is launched then the HMRC can demand any evidence to discount a fraudulent claim to tax.
You can keep any documentation in an alternative form such as electronic media via scan.This is as long as you can convert into a legible printable format.
There are some documents that cannot be stored in an alternative manner such as Bank Interest certificates, Dividend vouchers and CIS certificates(vouchers).