Clifton Lock is a lock on River Thames in Oxfordshire, England. It is located south of the village of Clifton Hampden and north of Long Wittenham. It is at the start of the Clifton Cut, which bypasses the river to the north of Long Wittenham.The lock was completed in 1822 by the Thames Navigation Commissioners. The main weir, which was built thirteen years later than the lock, runs across the old navigation of the river. A smaller weir runs just above the lock.