A sixth person, thought to be Australian, is still missing, The Guardian reported.
Philip Hammond said: "It is with deep sadness that I can confirm five British nationals have lost their lives when the whale watching boat they were on sank off western Canada on Sunday.
"My thoughts are with the family and friends of all those affected by this terrible accident. Consular staff in British Columbia are supporting the family members of those who have died and we will remain in close contact with Canadian authorities as further information becomes available."
The Leviathan II vessel went down apparently without warning about nine miles from the tourist town of Tofino.
