In message , Sparks
writes
Hello people!

We have just has some air conditioning installed at work.
When they wanted to join two pipes together, they used a tool to stretch one
of the pipes so the other pipe then fitted inside it, then they brazed it.

Can this sort of thing be done for normal copper water pipes for soldering?

Screwfix sell this
http://www.screwfix.com/app/sfd/cat/pro.jsp?id=15190

Am I correct in thinking this just spreads the very end of the pipe, rather
than stretching 2cms or so for another pipe to fit inside?
If so, where can I get the appropriate tool, or what is it called so I can
try to find one if they exist!

Err ... you posted a link then asked where you could get what was at
that url

When I replaced my boiler, I had one of these tools to hand - whack it
with a hammer - pipe fits inside pipe, job done

--
geoff