Hello Alan
I think the Essex regiment and the Oxford & Bucks must have some kind of connection, with soldiers going both ways, looking at grandads records he was also in the Essex regiment before joining the 1st Buckingham battalion (TA) in France in the middle of April 1940.

He was just in time to be chased halfway across France after it all kicked off for the BEF.
I'm quite pleased has it happens because I have just found a reference to him joining up with the BEF from the Essex regiment in the Oxfordshire & Buckinghamshire Light Infantry War Chronicle - Vol I 1939-1940.
Although hes not mentioned in person but with 50 others I will take that, its quite a nice mention as well which turned out true in his case.

all the best Adam
Thanks for the info Andy are these diarys you have got?