DJ G - it may be water causing the car to cut out but it also might be rust as well.
As the neck rusts, some of it falls into the tank and although there are filters in the fuel line they won't stop everything. I was sucking up rust and it was blocking my carb, causing the car to cut out just like you are probably getting.
Eventually I had a new tank and filler neck put on and also had the carb cleaned out.
Whatever work you do around the fuel neck area, I strongly recommend you pack as much Waxoyl into the area under the wheel arch as you can to stop it happening again.