I really sympathise with you, even though my situation is different. I moved back to my rural area in Wales a few years ago and the problem here is the opposite. I'm not saying that you wouldn’t be happier if you moved elsewhere, but it won't necessarily solve your problem as I have experience of both scenarios.
The community in the rest of the U.K isn't as transient as cities, which does help to provide some social stability, but that stability can also feel very inflexible and stagnant, depending on where you go. People do move in and out, but the people who've lived here form childhood get incredibly entrenched into their existing social groups. They don't like taking social risks, such as inviting a new person they've met into a social event with their existing friend group.
Therefore it feels impossible to break into the organic social scene, as opposed to more artificial /Meet-Up type gatherings. And that's a significant, but totally separate issue to the important one that @Marchitectmummy displays so well, which is that women beyond 30 simply don't have the time for new friends, especially if they have kids.
Like you, over the years, I've found meetups quite fruitless and pointless (and I did this a large city). People think they'd be filled with people open to friendship, but I've found that the reality is that -
50% have come long to just to their hobby and go home
30% are socially awkward, have possible mental health issues, or are just strange (and I have no patience left anymore to nurture such people or do the emotional / social heavy-lifting of keeping the conversations going)
20% are there hoping to make new friends....but obviously your personalities may not be compatible, so it's not a given that you will.
Before you move, just thought I'd share that I've learnt that repetition in key (especially if you want to befriend Brits). Turning up up to 5 times to Meet-Up is not enough. A lot of people seem quite socially fearful and unable to handle rejection, or rejecting other people, so they need to build a familiar with your face first. I'm afraid this has to be a minimum of 5 separate times, at the very least before they feel that familiarity, never mind think about having a proper conversation.