Just so I am straight, I take it that you don't use the last 20 metres of the lane? Who is the legal owner of the lane? Are you sure that your neighbour has been successful in claiming adverse possession of the last 20 metres of the lane?
I look forward to hearing from you.
Sorry- 2 last questions- do your Deeds grant you a right of way over the lane, or have you acquired the right by using the right of way for over 20 years?
If the right of way is mentioned in your Deeds, do you have a Mortgage over your property?
First and foremost, just because your neighbour has claimed possessory title of part of the lane does not mean that your right of way is affected.
(I must say that it is quite odd for your neighbours to have been successful in their application, as the Land Registry do not normally grant possessory title if it is clear on site or in the Deeds that a third party has a right of way over the land).
That aside, it is pretty straight forward for your right to be modified, so that it does not cover the last 20 metres of the lane. What needs to happen is that a Solicitor (this would normally be your neighbour's Solicitor) needs to draw up a Deed of Release which will set out that you agree to give up the part of your right over the last 20 metres. This Deed will need to include a Plan showing the extent of the right of way which you are happy to give up. The Deed is signed by both parties and is then registered at the Land Registry.
I hope this assists and sets out the legal position.
If I have helped, please could you be kind enough to leave feedback.