Most woodworm damage in UK is mainly caused Anobium punctatum, or common furniture beetle. It is found in Victorian properties, rarely of structural significance and is normally inactive – requiring no treatment.
Unfortunately, unless you can demonstrate inactivity it will be picked up by a surveyor or dap proofing contractor every time a property is sold, with an inevitable cost and renegotiation of around £500.
While guarantees are often waved around, these are fairly meaningless as the life cycle is typically 2 years. Therefore if there is activity, woodworm will reappear whether or not there is a guarantee.
So the solution is to paint gloss, resin or even paper onto the woodworm effected timber, to see if exit holes reappear within a year.
The profession treatment for woodworm is Permethrin. It is also the treatment for most insects including childhood nits. Toxic to insects, not so much to humans (see bottle for details).
If woodworm holes reappear, spray on Permethrin (£10) between February and August.