Neighbour's overflowing gutter causing leak into our lounge

itm2

For the last few years he have had a problem with water leaking into our lounge (through the middle of the ceiling). After first thinking that it was due to a leak in the flat roof above, we hosed the roof down and realised that it was in fact watertight. The problem was that, during periods of heavy or persistent rain, the gutter on the level above would overflow. This would eventually saturate the brickwork, and the water would channel its way through the walls and emerge in the centre of the lounge ceiling. We noticed that our own gutter was not draining properly, so had it replaced several years ago on the advice of a guttering contractor - this fixed a similar problem at the opposite end of the house, where water was leaking into my study, close to an area of the wall which had become saturated from the overflowing gutter. The issue was that the old gutter did not have a sufficient gradient to drain away the water properly.
The problem with the leaks into the lounge continued, however, and we realised that it was because the neighbour's adjoining gutter was overflowing, and saturating the wall below it (just above our lounge). We have repeatedly contacted the managing agent for the property next door (it's rented - I believe that the owner lives overseas), but each time their contractor has seen fit only to clear debris from the gutter, rather than replacing it and ensuring that there is a sufficient gradient to drain away water when there is heavy or persistent rain. This has happened three times in the last 16 months. 
Does anyone have any ideas for how we can get the landlord or their agent next door to fix this properly, as they clearly don't seem to be taking it seriously? We don't have the owner's contact details, but have repeatedly sent photos and videos of the problem to the estate agent who is managing the property, to no avail.

-taff

Have you gone through your house insurance? A few times of that may concentrate their minds...

itm2

Yes I phoned my house insurance today. They're sending a surveyor out on Sunday. At this point I'm not sure how it will help, as the cost of repainting our ceiling would probably not justify the loss of 30% NCD on the policy, plus I have an excess of £250 on water ingress claims. Since the gutter doesn't belong to me I can't claim for any cost associated with replacing it, which is the root cause of the problem. Also pointless redecorating anyway unless they fix the problem next door.

-taff

The other option I can think of is to take them to the small claims court for any expenses incurred so far [ did you say it had been going on for a few years? that's a few years worth of painting the ceiling?] You could send a letter from a solicitor to the managing agent to point out this is happening and that failing to remedy it is going to cost them via MCOL.

https://forums.moneysavingexpert.com/discussion/2208117/damp-caused-by-neighbours-guttering-help