I have no idea but aren't endowment policies supposed to be taken out at the same time as the interest only mortgage? not sure 10 years will cover that.
Yes, endowment policies were popular in the 1980's. You had two agreements: one with the lender as an interest-only basis; the other with an insurer for the term of the mortgage. When the endowment policy matured it should, in theory, have grown enough to cover repayment of the captial. Of course what really happened was that as the UK transistioned to a low-inflation economy the earlier projected growth rates turned out to be wide of the mark and people were having to make up the shortfall.
Wedrum, with an interest-only mortgage you really out to have been putting money into your chosen repayment vehicle from day one (and tbh, most lenders these days want to see evidence of this). With only 10 years left, you're going to having start saving hard. Alternatively, if you think you really can't make it in time, consider switching all or part of it to a repayment mortgage.
Best advice, speak to your mortgage lender now.