Just checked the highways agency website as there is a lot of roadwork's going on at jt 12 Gaydon for the Jaguar land rover employee's which results in the slip roads being closed in both directions from time to time.
it is saying both North and South bound slip roads will be closed all day.
so its get the map out and allow a bit of extra time to get there. 
 
Paul   

Those coming up from south will be OK as they can get off at Banbury junc 11.  From Midlands and north probably simplest to go further down to junc 11 and then come back.