Remember, Tennessee, Mississippi and Texas already have similar laws in place in the US, so even a nation with better speech and gun laws is still not immune from the slow descent into technocracy.
If the 'political speech' is not adult in nature, which is true 99.9% of the time, then it can't/won't be blocked under this rule.
Unless of course this political speech is happening on a porn site, or a subreddit that has been deemed 18+. Which I can't see a legitimate reason for.
A lot of LGBT content is aimed at adults. I think we should always be clear when we are making statements like this because it causes great stress, a worked example:
People will claim that LGBT is under attack because this law potentially affects some LGBT spaces. These spaces will clearly be meant for 18+ audiences and so fall correctly under the law. Then other people see the first group of people, and from their point of view that group is complaining that their 18+ spaces are blocked from children. "Think of the children" drama ensues.
It is similar to Steam taking down incest/rape games and people claiming it was an action against LGBT creators. I don't think that's an argument that should ever be made for obvious reasons.
I don't think the government, even if it were under the Conservatives, have banning gay spaces on their current agenda.
I simply don't want to be forced to provide my ID / face to be able to read or access politically important news on social media. Some people would be happier if the bill was limited to only pornography: they likely don't think it has a major effect on UK politics.