Damage from neighbours leak

In August 2018 I noticed water coming over my drive from my neighbours property (the 2 properties are separated by a hedge, and each of us have a driveway, but their property is on a higher level than mine by about 2-3 feet). I telephoned the water board straight away and notified the owner's daughter who lives there (her father owns the property but is 92 and gets confused). She said she'd thought they'd got a leak a few weeks before but didn't do anything. I was present when the Water Board discovered a leak of 8 litres per minute from their property on 10 September 2018. To date nothing has been done, I have tried complaining to the Water Board in desperation but obviously because its on private land the Water Board are not responsible. Because my property is on a lower level, the water is constantly seeping on to my property, which has caused the tarmac on my drive to disintegrate and pot holes develop, with cracks to concrete beneath it. The drive is constantly wet up to the outside wall of my property and in places is covered by a film of sludge, I have mobility problems and I slipped and almost fell because of it a few weeks back. More worryingly is the unseen damage this is causing to my property. I have spoken to the daughter but she blames the Water Board and keeps saying she's waiting for them to get back to her. I cannot believe someone would allow so much water to be wasted for almost 2 months now. The whole business is making me ill. It looks like the only way I can get anything done is if I claim on my insurance, there is a £300 excess and of course my premium will go up. Does anyone know if I would be able to get this back if I take them to a Small Claims Court? I'm now thinking of selling next spring, and I would have to declare any neighbour disputes if I went down that route. Has anyone had any similar experience or any ideas?