We have a completely flat roof on our terrace house. The water is supposed to drain down next doors drain, but this is often blocked and then we get leaks, we go up and clear the drain and then its ok, but this is a pain and we're getting older. Is it easy to fit our own drain or is there some kind of pump which would solve problem. The existing drain next door is internal so we would need to go through a wall or over parapet.
As Welsh brickie said, you can add another one or two outlets and install a leaf guard in combination with a wire balloon to solve your problem -- it would be a permanent solution too (until we get our typical british weather battering us down.)
JJ Roofing supplies offer nationwide delivery on these products and can be picked up relatively cheap, I stand by this company and recommend them hugely if you're going to purchase a roofing product as I have had great luck with them in the past.