If I buy a used anything, it's up to me to check what I'm buying (and
the correctness of any bonus documentation). I don't see why that
should be different with a house.

That is why it is wise to pay for a full structural survey. If it does not
reveal the nasties you have an insurance that will pay for the problem to
be rectified.

I'd say the onus is on the anus who
did your survey to give you back his fee.

If you had the right kind of survey. If you did not then you have no one to
blame but yourself.
That is indeed what I am also considering - if all I need do is put an RSJ
in for support then I shall do it, however I also feel a need to get the
lying *******s back who did the work in the first place - if I can get the
proof I shall do this. If I have no proof then I also can't truthfully
say
anything about the conversion to a prospective buyer.

Far from it. The fact that the RSJ has been put in by you is proof that you
did know there was a problem.

Peter Crosland