An Income Payment Order lasts for three years. The ISI's guide to bankruptcy says that an Income Payment Order "ideally should be agreed to at the earliest stage of bankruptcy. This is to ensure that you as a bankrupt person are subject to it for the shortest period possible after your bankruptcy has been discharged".
The ISI's guide to bankruptcy can be found at [broken link removed]
The quote is from Page 11 where it also says that an Income Payment Order lasts up to three years.
Paying an IPO for four years in total doesn't sound right. It may be a clerical error on the part of the ISI and your relation should push back and say that he/she will only agree to three years of payments, one year during bankruptcy and two years after bankruptcy.