When is abortion illegal?

I ask because the BBC is reporting the Department of Health is investigating claims that abortions have been carried out based on gender which in the UK is illegal. Now I hadn’t really known that and had rather assumed that you could have an abortion if you wanted and that was that, which is fine by me. I had a vague idea that some women might have to undergo some counselling before being allowed an abortion, but really that was it. Looking on the Marie Stopes website at their Abortion Facts page the process appears even simpler. So the answer to my question when is abortion illegal? Abortion should be legal and that’s it no added caveats.