I cannot see any reason for informing the revenue as this contract is the same as a pre-gross roll up contract in this country. Providing that the policy is with a uk onshore comany and you did not request the fund to be altered to have offshore status, I don't even think an onshore endowment would even facilitate this, the fund is being taxed within the company annually at Corporation Tax, which deems that the policy holders income tax liability is satisifed. There are other rules in the uk in relation to qualifying policies and if you break the qualifying rules you could deem the benefit to be taxed at marginal rate, if you have left your policy to maturity you have not broken any qualifying rules.
In saying all of this, if I were you I would keep bankstatement on both sides of the water to prove that the monies were transfered from taxed monies. Better to be safe than sorry with the revenue, you can see what they are doing now in relation to the Single Premium Investigation, the onus is on the tax payer to prove the source of the monies. You are supposed to inform the revenue in the event that you make a gain on items, even on your ppr you are supposed to tell the revenue when you sell it although no one really does, in this case the policy is maturing so no sale but you are (hopefully) making a gain, but as the income tax liability is satisifed there is no CGT liability so no need to inform under gains made IMO.