When I produced my comprehensive (ahem) treatise on tablesaw use on DVD nearly a decade ago now, I consulted the HSE, just to make sure I wasn't making any major boo-boos. They confirmed what I already knew.
1. Dado stacks are not illegal in the UK, neither to sell nor use.
2. What IS illegal is:
a) To use a TS in a commercial workshop that is not adequately guarded. Unfortunately the standard guard that comes with most TSs has to be removed as it is usually mounted on the riving knife. So some other suitable guarding has to be devised.
b) To use a TS in a commercial workshop that does not stop within 10 seconds of the power being cut. The increased mass of the stack c.f. an ordinary blade means that the momentum of the revolving blade keeps it moving longer than a normal blade. On a small light, saw, this is significant. On a bigger, more massive saw, the extra blade weight is of less significance.
I have an Xcalibur cabinet saw, sadly no longer available. It came with a short 30mm arbor and a long 5/8" arbor, so it will, and occasionally does, take a dado stack.
But it still stops in under 7 seconds, even at full stack, and I have devised a range of guards for use with different sawing operations, including dado stacks. I NEVER use my saw unguarded, whether the camera is on or not.
I'm not aware of any other saw available in the UK that will accept a dado stack, although I believe that one of the top-end Scheppach saws does take some sort of grooving blade (though I don't think it is a stack).
Dado stacks produce very clean cuts, but the setup time and faff is only really worthwhile for production runs. There are usually other methods, quicker to set up, that achieve the same end, and are more suitable in the home workshop for one-offs and small runs.
If you do use one and use it for rebates and cabinet backs, I highly recommend my
rebate and groove fence. But then, I would, wouldn't I?