No car-pool lanes in the UK that I know of.
We have websites where you can offer/request lifts, eg
https://liftshare.com/uk . Works for one-offs and regular journeys.
Otherwise, I'm happy to offer lifts, just as I accepted them in my youth. And I have tried hitching since, when I was trying to get to a medical appointment and the buses had been re-routed - ended up calling a friend.
The latest people I picked up were a couple of French, who'd hoped for a ferry on a Sunday. They now needed to use the much longer road route.