Mmmm Not aware of any rear wheel bearing which is adjustable. For your Meriva, I believe, it's a bearing kit assembly you require, £50-60 a pop, don't think you can easily split old assembly and replace bearing. I'm assuming one of your rear wheels is "rumbling" !!!
That's about it .A lot of the older cars had adjustable bearings, only a few left now I'm afraid. For £60ish It's not worth the hassle of trying to split the bearing , even if you can. Real pain without the proper equipment.