I suspect that this is a bond that aims to track the FTSE using a combination of cash, gilts and options over a fixed period of typically 3.5 or 5.5 years. Basically they advertise that you invest (say) £10,000 which is guaranteed to be returned in full at the end of the term, plus a %age of any growth in the FTSE. If the index crashes then you still get back your £10k.
What happens is that 5% is deducted to pay commission to the introducer of the business. A further 4.5% (ish) per annum is then deducted and used to buy some call options. So for a 3.5 year fixed term, about £1500 is used to buy call options with 3.5 years to expiry. The balance of the investment is put in cash or gilts and the interest is used to bring the balance of the original investment back up to £10k by the end of the term, so is never actually exposed to the stock-market. If the index rises, the profit comes from the call options. If the index dives, then the calls expire worthless, but by then the capital is back up to £10K so you get your original stake back.
Some of the older style bonds were known as "precipice bonds", because you only got all your money back provided that the FTSE never dropped by more than a fixed %age (typically 20%), and if it did, then there would be a progressively increasing loss of capital. This is because in addition to buying call options they also sold put options about 20% below the market. Provided the FTSE never fell more than 20% then they would expire worthless and all the premium would be kept, but a larger drop would leave the short puts "in the money" and the loss would be deducted from the capital. These "precipice bonds" have largely been discredited now because so many got hit by drops in excess of 20%. With some, losses if the index dropped by more than 20% racked up at 3:1 so you could lose your entire investment with a 33.3 % fall in the FTSE - and some people did!
I guess these types of product have their place, but as the capital is never actually invested in the stock-market there are no dividends. If the FTSE is yielding 4% in dividends, that means that over a 5.5 year period you are foregoing 22% in potential growth. A large part of the growth in a long term investment comes from reinvested dividends, so my view FWIW is that you'd be better off investing in an equity income fund, or a portfolio of self selected high yielding stocks, and accept the risk!