Your LP10 will be worth whatever somebody wants to pay for it at the time ( as always) and this can vary quite a lot but the LP10 is a very popular pistol and even the older non ball raced trigger type should fetch a minimum of £650 if it is in its original case and in good condition with handbook, tools and filling adaptor etc.
Most buyers also want to know the date stamp that is on the two cylinders as it may give some idea of the pistols age.
Some pictures of your LP10 would help to give a more accurate valuation and it would be good to know if it is the silver or black version.
Good luck with your sale - if the price is right it will sell quickly
Rossendale Target Shooting Club. Every Tuesday and Thursday evening 7 - 10pm.