I just noticed this on Lastminute.com, it's seems quite a good deal, seeing as if you were to go just in the peak season, a ticket would cost you £24.
Terms and Conditions:
Half term (February 16 to 22), February 28 and March 1, 7 & 8
* Two day ticket - visit on above-mentioned dates & come back again before the end of June and get the chance to ride the new Saw the Ride in main season (starts from March 20). This offer excludes Easter weekend (April 10 to 13) and May half term (May 23 to 31)