about an aborted foetus that comes back to kill the people that did the deed.

It's called

"Sewer Baby"

Not making this up. My housemate has it on VHS and it's fucking hilarious (if you can stomach such things/are sick enough to find it funny)
Highlights include:

* The abortion being performed by a fag smoking, dirty grotbag of a 'madame' with a coat hanger

* The foetus being flushed down the toilet

* The climatic end where it tries to get back into his mummy's tummy by tearing through her vagina

Barry Norman has never reviewed it, to my knowledge.