I'm not an expert on such matters, but have been looking into similar
things
myself recently. I can't see anything in building regs which
specifically
says you CAN'T run SW to a FW drain, however reading between the lines I
doubt it would pass building regs, if inspected - I doubt the water
board
would be too happy either. Building regs says surface water can run
into a
drainage system, whereby a rainwater drainage system: "carries the flow
of
rainwater from the roof to an outfall (a soakaway, a watercourse, a
surface
water or a combined sewer)...".

I suppose the biggest risk is the FW sewer overflowing in torrential
rain.

It is permissible, but only as a third choice, where the other options
aren't "reasonably practicable".

http://www.odpm.gov.uk/stellent/grou...s/page/odpm_br
eg_600283-05.hcsp#P1601_100217

Is this not clarified by point b.i. below that though - where it qualifies a
sewer as "a surface water or a combined sewer" - i.e. no mention of a foul
water sewer, so therefore it wouldn't meet regs?

Andy