Interesting Who casting spoiler

Pointed out by jinxed_wood and ( spoilerific )

FTSE?

I'm looking at buying a 6-year ISA which pays 40% if the average value of the FTSE over the 6 months at the end of the period is higher than it is at the beginning - if it's lower I'd only get 2%.

FTSE Graphs I've looked at show a general upward trend, a drop at the end of last year presumably caused by the bank crash, and what looks like the start of another rise.

My thought on this is to put about half the money I'm investing this time round into something that has a guaranteed interest rate, and the rest into this one since there's the risk of a low payout. Anyone got any suggestions, or any reason why the FTSE one isn't a safe investment?

Later Having taken on board what people have said here, I've decided to go for an index-linked ISA which has a minimum 18% payout. I have enough in easily-liquified savings that I'm not too bothered about that side of things, my main aim here is to maximize my savings for after I retire. The 40% thing is too much of a gamble.