You are now required by all Insurers to supply your ERN No. when arranging Liability Insurance. This is essential to assist future claimants who in the past have had trouble in ascertaining who the Insurer was at the time of a specific potential claim. Remember someone could claim for say RSI ( repetitive strain injury) but the problem may only reveal itself many years later. So in essence you must supply your ERN (Employers Reference Number) as supplied to you by HMRC it could save you lots of trouble later on..