As far as I recall a standard endowment mortgage guaranteed to repay the loan, but made no promises regarding any bonus, the providers were allowed to use a certain maximum percentage in their 'what if' scenario spins.
The much touted 'Low Cost' endowment mortgage assumed a certain minimum growth in value over it's term, thus providing possible repayment of loan and maybe a bonus, all from lower charges !! More dosh required if the plan was falling behind. - Not a good buy, but if this was the only mortgage one could afford... in the 80's or so, then no doubt the explosion in property prices helped a little - in the shorter term.
Also, way back one received tax relief on the total interest paid per annum at one's highest tax rate, a nice little earner that, an endowment charges interest on the full capital amount borrowed throughout the term - so the tax relief was more or less a constant. Until successive Govn's moved the goal posts.
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