I am looking for a table showing attenuation (in dB) building
materials (concrete, plaster, steel, glass, wood etc)for signals in
the Med/Low VHF range (47MHz-85MHz [UK Radio Microphone frequencies]).

Thanks

I don't know these figures, but I doubt you would find them useful to
your practical problem with a Radio Microphone.  Obviously, sheet
metal has enormous attenuation to radio waves at VHF, non-metalic
substances usually not much.

In practice the biggest screening effects are likely to be caused by
electrical wiring within walls, and water and gas pipes.

You might be able to solve all problems by connecting a "leaky feeder"
to the receiver antenna input.  The "leaky feeder" would comprise a
cheap coaxial cable with a widely-spaced braid, so that it acts as an
antenna throughout its length.  Run the "leaky feeder" around all
areas where you require reception, and terminate the end with the
standard antenna.  Hence the longer the "leaky feeder" the better for
your purpose.  Try cheap 75 ohm coax from Tandy.

Radio propagation effects indoors are a big can of worms.  The
material absorbtion component is the least of the challenge (as sorwin
is aluding to).  The shapes of metallic objects in the neighborhood is
a big issue.  In some testing I've seen, the corner of a square filing
cabinet can wreak havoc on radiation patterns.

This is why most serious radio system deployments involve a serious
site-survey with engineers, antennas, spectrum analyzers etc to ensure
that the space is understood, and antenna placement manages the
challenges.

-Rossgk