“downhill without the jumps” is a wee bit of an odd comment, what you get if you take the jumps away from downhill, is downhill. But then there’s no red line between downhill and just riding your bike. TBH most UK downhill could be used for enduro racing, many already have.
Antur Stiniog is extremely trailbikable, but also very trailcentrey, super-manmade so doesn’t tick my enduro boxes. Very good, though. Fort William red as mentioned is ideal, the world cup route is a bit harder but still goes on a trailbike as long as you’re a reasonable bike handler- there’s some big jumps at the bottom but they’re pretty ignorable. (if I can do it, then it can’t be that hard) And BPW of course, custom built for what you want.
Glencoe, the red last time I rode it was underwhelming, the dh is pretty bloomin alarming and I’m told now in a bad state of repair, and the uplift is poor- bad bike mounts, bellend staff. Certainly wouldn’t go back there for a trailbikey day.
Innerleithen’s the obvious one though- the purpose-built enduro trails mostly start from the top of the downhill, most of the downhill trails fit the bill perfectly. Only downside is that the uplift doesn’t go all the way to the top and isn’t the fastest or the most frequent, but then if you can ride to the top 8 times in a day more power to you. Oh, and if you do the further out or slower trails it’s a race to get back before the bus leaves.