After investigation I've found the soakaway/French drain that my roof guttering exits into has become ineffective - the water from the down pipe doesn't actually drain away - indeed in the recent heavy rains it backed up, in the down pipe, to the roof level! The situation is made worse as my down pipe is the only one for the four houses in the my terrace.
My question is are you allowed to route the rainwater from roof gutters into the normal household drainage system (where sink, bath and toilet waste water goes)?
The external man hole cover is just 4 foot from the down pipe. It would be a much simpler job to route the roof gutter pipe work into the standard drains than create a big enough soakaway to coupe with the amount of water from the 4 roofs.
I also faced a similar problem recently. I contacted my local water authority for clarification (Anglian water). They advised that surface water drainage into a foul water sewer is not permissible. You have to run it into the nearest surface water drain, if there is one or else into a soakaway. In my case there is no surface water drain provided so I was stuck with creating a french drain/soakaway. The fine for running surface water into the fould sewer is circa Â£10,000!! You can imagine that pumping stations and sewage works would become quickly flooded or unable to cope if surface water as well as sewage were routed to them.
My situation improved greatly when I started digging around the bottom of the down pipe. 3 feet below the soil surface (2 feet from the bottom of the down pipe) through hard compactted soil and stones I found the pipe entrance to the soak away, which wasn't actually blocked - it looks like who ever replaced the down pipes/guttering last didn't sort out the area around the bottom of the down pipe and soak away entrance and the water basically washed the soil and stones from the surrounding area into the hole blocking access to the soak away - I made a small chamber out of bricks and cement around the soak away entrance to keep the soil back, since then all the water has been disappearing without any problems - a huge relief. :-)