Hello and thanks for using Just Answer.
I am Al and am happy to assist you with your enquiry.
Provided the encroachment has been in place for 10 years or more, then you would be entitled to apply to the Land Registry for "possessory title" of this land.
Basically, whenever a party possesses land which does not belong to them legally, they can claim ownership of it, if the possession has been undisputed or without the consent of the true owner for at least 10 years.
Making such an application to the Land Registry will take time and it may be best for you to try and come to an agreement with your neighbour- it would be easiest for him to willingly agree to transfer this small section of land to you, and which paperwork could be prepared by your Solicitor. As a sweetener, you may wish to offer to pay your neighbour's legal fees in doing this, if indeed he agrees to it. Having said that, if he were to go to a Solicitor, he will be advised that there is little he can do to demamnd a payment/request demolition if your utility has been in place for over 10 years.
I would therefore suggest that you explain the above to your neighbour and see what agreement you can reach. You can of course inform him that you plan to apply for possessory title and hope that a resolution can be found.
I hope this assists and sets out the legal position.