So have been doing a bit of plumbing recently to install a new hot water
tank and tidying up a lot of old stuff leftover from what appears to
be many years of job on job on job ... And I've found quite a few pipe
joins that are made without a sleeve - they have expanded one ond of a
pipe just enough to push the next section in, then solder.

Is this a technique of olden times as I'm not sure I've seen it before.

It does seem to make for a neater join with only one soldering required
as opposed to both sides of a sleeve... Is there a magic tool to expand
the end of the pipe without it splitting?

Cheers,

Gordon