I can't speak for the UK but in Belgium it's certainly illegal to discriminate based on gender, age, race, ....
There was even a case recently where a man won a lawsuit because he was excluded by a clothing store that was searching for a female employee for doing an inventory job.
"Brussels, 23 August 2018 - The legal action taken by the Institute for Equality of Women and Men reminds employers that sex is not a criterion for refusing an application. The Leuven Labor Court has sentenced a clothing store to discrimination based on sex. He refused a man's candidacy because he wanted to hire a woman."
That being said I also seen adverts asking for women but technically it's against the law and even with all those laws discriminations happen more often than not.
There are exceptions like modelling or acting where roles where there could be reasonable reasons for being gender-specific but not for the tech and public sector jobs described in the article.
Given the way issues like this overlap with the European Convention on Human Rights I would expect it to be very similar across Europe (certainly within the EU).
