What's that flag?

Mother lives in a flat just off Grand Avenue in Worthing. It's a wide road ending up at the sea with steps and a semi circular end as if there was once a grand  "something" at the end of Grand Avenue. Today I noticed a Canadian flag and find there is a memorial to the Canadian servicemen who manned a large gun at this position during WW2 to defend the South Coast. Apparently the flag was hoisted in 2012 but  today was the first time I noticed its lovely red against the grey sky,.