Yeah, it's more common than you'd think—lots of companies do block-book events months ahead, even off-season, especially for team socials or early Christmas do’s. I had the same issue and found that midweek afternoons can sometimes free up last minute, though you've gotta be quick. Also, keep an eye on https://spinnersuk.com/ since they sometimes drop extra slots or limited-time packages that don’t get flagged on booking sites.