The concrete vessel on the right is CRETACRE, which was owned in West Mersea from 1933 to 1938. Ron Green can remember staging or seating being fitted on deck before she went away, to be used, he thinks on the Thames as a grandstand for the Coronation or Jubilee in the 1930s. Don Procter says she was towed away by a trawler, which does not tie up with the tug shown in this photograph.

Most of the following information is from a website that has now vanished:
CRETACRE barge Official No. 142652 Completed 1918 by Hill, Richards & Co., Hamworthy, Poole. 664 tons gross. [ The 1919 Mercantile Navy List has her as CRETACRE but some sources give her name as CRETEACRE ].
Owners:
1918. Completed for The Shipping Controller, London, U.K. as PD 25.
1920. Samuel Dowding , Southamton, U.K.
1930. William O. Cooper, Southampton, U.K.
1933: West Mersea Lighterage & Towing Co. Ltd., West Mersea, U.K.
1935: Company renamed West Mersea Docks & Engineering Co. Ltd., West Mersea.
1936: Clarke & Carter, West Mersea, U.K.
1938: New Medway Steam Packet Co. Ltd., Rochester, U.K.
1941: Sold to U.K. Government.
1942: Kite balloon tender at Southend (www.naval-history.net)
1948: Reported demolished.
[Thanks to David Asprey for help with these details].

There is more information on these barges at ww1poole.wordpress.com/2018/10/24/the-first-concrete-barge-to-be-built-in-britain/ [Apr 2021]
Date: c1935