.Thank you question. My name is ***** ***** I will try to help with this.
You have a claim against the neighbours in common law negligence and common-law nuisance in respect of the damp and the damage to the property. If they will not remedy the problem you will have to take them to court, firstly order to make them put everything in good order and secondly cost of repairing any damage to your property.
If the soak away you mention will resolve the issue but they will not pay , you can have that put in place and then sue them cost and the cost of putting right any damage.
I suggest that if you have house insurance you have a look at the policy because many such policies have legal expenses insurance attached to them which would pay the legal costs of taking the neighbour to court. Before doing that a letter from a solicitor may avoid the need to go to court because the solicitor can threaten the court application and suggest that the neighbour takes legal advice. If the neighbour does take legal advice they will be told that they are going to have to put this right or face court proceedings and legal costs.
Can I clarify anything ?