I admit that I've only ever done it with single cables. One 2.5mm fits fine into a 15mm pipe, and 1mm (perhaps also 1.5mm) into a 10mm pipe.I wouldn’t. But, it could so long as it was really obviously feeding a socket and not being a pipe but you wouldn’t get 2x2.5 down a 15mm pipe so you’d need a 22 which is obviously bigger than 20mm conduit.
There are various ways it can be done with plumbing fittings. I only seem to be able to find a compression one of these, but a solder (and less battered - sorry about the one I found!) version of this looks much better and, with an appropriate nut (albeit it screwed tightly into a 20mm knockout!), does the job (and solves the earthing issue) ...On top of that, you would struggle like crap to make the tube off into the socket. And you’d need to Earth it
[See missing photo in next post!]
I've even been known to do it with a modified SWA gland, but that (like the compression fitting) is not too pretty.
Kind Regards, John