This is what the insurance said:
"In any consecutive three-year renewal period You may incur Two unlimited Third Party or Accidental Damage claims without impact on Your No Claim Bonus entitlement.
However, where You incur more than two of these unlimited claims in any consesecutive three-year renewal period, Your No Claim Bonus will step-back by three years.
In addition, any claim payment for Windscreen Breakage, Fire or Theft will be paid without impact on Your No Claim Bonus entitlement."