"Damp" (condensation?) wall

Hello,

A brief description. The lower part of an internal wall in a purpose
built flat is suffering from "damp". The wall paper has lifted way.
there is no mould growth.

Now I have borrowed a Protimeter (damp meter) from a surveyor friend
, taken about 100 readings and I am reading the excellent "Dampness in
Building" Oxley / Gobert ISBM 0-7506-2059-5.

To summarise what I have found.

The wall is 7.60m long, 2.35m high. It is a "shared" (with adjacent
flat) internal wall, probably load bearing as concrete lintels cross
it at right angles. The composition is (probably) brieze block with a
plaster skim (as in rest of flat). There is a soft-wood, 9cm skirting
and the floors are solid concrete skim with vinyl tiles. On top of the
tiles is Dunlop underlay and wool/nylon carpet.

Left-Hand end of the wall is adjacent to the front door that opens to
an internal hallway in the block, not directly outside. Right-hand end
of the wall is adjacent to, and at right-angles to, another internal
wall that is tiled bathroom wall on the other side.

I have taken "damp" readings at 25cm horizontal intervals and 10cm
vertical intervals (what a tedious job !!).

Results: At LH end by front door, the skirting and wall register
between 11 to 13 – this is not a concern to me.

One third of the way from the RH end, opposite a large
double-panelled radiator the damp registers as follows.

The skirting measures between 17 to 24. The skirting is more damp the
closer the reading is made to the junction with the floor.

The wall immediately above the skirting measures between 20 to 50.
The highest wall reading occurs directly above the highest skirting
reading.
Question: Could the high conductance be due to damp wall-paper rather
than the plaster?

The damp reading diminishes rapidly vertically to a level of 12 to 14
at a height of 30 cm. This value is for any position along the wall,
including the most damp areas just above the skirting toward RH end

At any height above 30cms the wall measures 12 or 13.

Initial thoughts

1. The radiator is causing the problem. But how? And what to do? I
can't move the rad.
2. Damp is coming from the floor. How do I investigate that further?

Any ideas on what to investigate next to try to isolate the problem
before I call someone in who may attempt the wrong treatment because
they haven't understood the cause ?

Many thanks

Clive