Folks-
Michael Yon has written about this on his fantastic online
magazine/journal/blog.
“Please have a look at the attached from the UK Times. Regarding the Rachel Sylvester piece, we have not been able to find any such document/memo although it is possible that an e-mail exists somewhere that refers to such a matter – more likely to be a warning not to dick about regarding what extra troops the UK might be able to find for AFG and raise unrealistic US expectations.”
Taken from the email he was sent by a "well placed British officer".