The honest answer is not a lot
If selling privately it would be worth anywhere between £400 & £800 depending on overall condition, length of Tax & MOT, condition of tyres, service history, etc. Unfortunately older petrol engined 4x4's are not particularly popular as a second hand buy.
If your looking to replace it with a brand new car you'd be better off using the government's scrappage scheme at which point it's worth a minimum of £2000, with some manufactuers it's worth even more as some are now offering increased discounts in the run upto Christmas.....