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Hello and thank you for your question. I will be very pleased to assist you. I'm a practising lawyer in England with over 10 years experience.
I am sorry to read of the above. Do you happen to have a copy of your lease to hand?
Many thanks. If you can leave that with me for a few minutes and I will revert.
Sorry for the delay in reverting to you. Thank you for the copy extract of the lease. Obviously this is not the whole of the lease but fro what I can see it includes the relevant sections which would contain covenants preventing you from subletting under Airbnb though there are some more restrictios referred to in the first schedule.
Renting out the flat on Airbnb or similar would be breaches of clauses 3.7 (due to the decision in Nemcova v Fairfield Rents Ltd  UKUT 303 (LC) and also clause 2.6.3.
However the landlord is not entitled to damages arising out of your breach of covenant. His remedy is to serve you notice and require that you undertake not to do so again. Given that you are no longer breaching the covenant it would be bold for him to serve a notice of breach of covenant now but technically he could. The worst that could happen is therefore that he serves you with a notice of breach of covenant and claims solicitors costs for doing so which might amount to £2-300+VAT. That in itself would be extremely draconian if you make it clear in any disclosure to him that you have long since ceased to breach the covenants above but he could argue it being valid service.
Otherwise there is nothing more he can do. So the neighbours threats do not have a great deal of weight. If you feel that your neighbour may contact our landlord you may be better to preempt this by disclosing the breaches of covenant making it clear that you have not done so since [date] and undertake that you will not do so again.
Otherwise as you say the neighbour would need to prove negligence in order to make a claim for damage caused as a result of leaks.
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A pleasure. No the presence or not of guests would not be material. What is relevant is the cause of the leak - if it was due to negligent disrepair (i.e. you know something is faulty but don't bother to fix it) or leaving a tap running and water overflowing - this would be negligence and your neighbour would be entitled to damages. However your neighbour has to prove negligence. An accident - e.g. a pipe bursting which was not known to be faulty is not negligence and she would have no claim against you.
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