FIA wishes to know if "this allegation has any basis in fact"

[Bob Dubery]

The text of the letter recently sent by FIA to F1 teams is viewable at
http://www.grandprix.com/ns/ns19605.html

Note...
'The FIA has subsequently been made aware of an allegation that one or
more McLaren drivers may be in possession, or that such drivers have
recently been in possession, of written evidence relevant to this
investigation. In the interests of the sport and the Championship, it
is important that the FIA, as the regulator, established unequivocally
and rapidly whether this allegation has any basis in fact. The FIA
therefore formally requests that you produce any documents which
involve, relate to or were sent by or to any McLaren driver which may
be in your possession or power of procurement and which may be
relevant to this case. '

There follows a clarification (well it is the FIA) of what is meant by
"document".

This is level-headed and proper behaviour on the part of FIA. A
serious matter has been investigated. The original hearing left the
door open for the case to be revisited if new evidence appeared. Now
some party has alleged to the FIA that there is more evidence and that
a McLaren driver or drivers have or recently had such evidence in
their possession.

Quite right that the truth of this allegation be tested.

Presumably the identity of the alleging party will be revealed at the
WMSC hearing. Unless, of course, it is deemed to be "whistle blowing".