From the M4 (Newbury and Didcot), exit onto the A34 northbound towards Oxford. Leave the A34 at the Marcham Interchange and follow the signs towards the A415 (Abingdon Town Centre). Follow the A415 (Marcham Road). Go straight ahead at the first roundabout and turn left at the next roundabout. Take the first turning on the left (shared driveway with McDonalds) and the Brirish Red Cross building is on the right.
From Oxford, take the A34 southbound and follow directions as above from the Marcham Interchange.