The consortium have, historically, always been around the first week of November... with the exam for entrants who do not attend a slough school being on the Saturday.
I have had a trawl thru and found this..
Thursday 4th November 2010 (for slough schools)
Saturday 6th November (for all other children)http://www.st-bernards.slough.sch.uk/?page_id=349
Click on link for 'Admission Open Evening 2011'
St Bernards is part of the same consortium as Herschel therefore I would think this is the 2010 exam date for 2011 entry.