The claim made in the title of this thread - "Staring' at women is now illegal on the London Metro" - is not accurate.
Staring at someone (of either sex) in a way that is sexually aggressive, bothersome and intimidating on London transport is one of a list of several commonplace behaviors that Transport for London has targeted in a campaign that aims to reduce sexual harassment by bringing greater public attention to the many "normalized" acts that constitute it. But because most of the sexual harassment that occurs in public places like the tube, buses and waiting areas is committed by men and boys against women and girls, the campaign is focused on making taking public transport more comfortable for female passengers by drawing attention to unpleasant, sometimes criminal acts that females tend to be subjected to by males. From the press release announcing the project:
The campaign highlights various forms of unwanted sexual behaviour that can take place on public transport and aims to send a strong message to offenders that sexual harassment is not tolerated on TfL's services.
The campaign aims to challenge the normalisation and dismissal of this behaviour as 'something that happens' to women and girls on public transport and in other public spaces, making it clear that it is never acceptable and that the strongest possible action will always be taken.
The following behaviours are highlighted by the campaign as common examples of sexual harassment, which are not tolerated on public transport:
1. Cat Calling: Making unsolicited remarks of a sexual nature about someone
2. Exposing: Revealing intimate body parts [aka flashing or indecent exposure]
3. Cyber-flashing: Sending or showing sexual content without consent
4. Pressing: Rubbing against someone on purpose [aka frottage or humping]
5. Touching: Touching someone inappropriately [aka groping]
6. Staring: Intrusive staring of a sexual nature
7. Upskirting: Taking photos under someone's clothing
Behaviors 2, 4, 5 are already illegal and criminal under existing laws against indecent exposure and sexual assault. 3 and 7 are illegal under newer UK laws that prohibit the use electronic communications and recording devices in certain ways.
But AFAIK, 1 and 6 are not illegal under UK law. Rather, the TfL wants to make it known that they are unacceptable and "not tolerated" on London public transport.
At any rate, "staring at women" on the tube or other kinds of transport in London certainly not been made "illegal."