Thank you for your replies.

In answer to your questions:

He never mentioned the pipes when quoting or installing the radiators.

The end radiator does get very hot if all the other radiators are
turned down to half heat. Does the balancing result in being able to
have all the radiators on full? I was kind of hoping to be able to
heat the whole house at once!

I will certianly report this guy to the IoP. He is pretty aggressive
when we try and talk to him about these problems and keeps saying it
must be a problem with the old system, when he's changed everything
except the pipes.

I assume that padding the pipes is relatively simple so I think we'll
give that a try. Any words of wisdom about the best way to lift the
floor boards (not tongue and groove) and which padding to use?

Thank you again

Victoria