From the Wikipedia page 
Sunbury Lock is a lock on the River Thames near Walton-on-Thames in north-west Surrey. The lock adjoins the southern bank about half a mile downstream of the Weir Hotel.
There are in fact two locks, which are some distance downstream of the original lock built in 1812. The older hand-operated one was originally built in 1856, but is now seldom used. The newer one was opened in 1927 by Lord Desborough. There is also a slide for the portage of small boats. The lock adjoins Sunbury Lock Ait.