Paul,
I've struck solid 2.5mm here a few times in houses built or re-wired during the 60's.
I think that the first white sheathed TPS (Tough Plastic Sheathed) cables that came out here were all solid or the cable was imported from the UK.
Stranded cables make the task of terminating wires a lot easier, especially where there is more than one wire in a terminal.
Oddly enough, I happened to strike some 1 mm stranded TPS in a house here recently, I didn't like the look of it either, it looked really cheap and shonky.
