LONDON, July 7 (Reuters) - Britain's opposition Labour Party will call a no confidence vote in the government when it believes members of the ruling Conservatives will support it, the party's trade spokesman Barry Gardiner said on Sunday.

Boris Johnson, the frontrunner to become prime minister this month, has said Britain must leave the European Union on Oct. 31 with or without a deal. Several Conservative lawmakers have said they would consider voting to try to bring down a government which was pursuing a no-deal Brexit.

"We will call a no confidence vote when we believe that those Conservative members of parliament who have said that they would support a no confidence motion in the government in order to stop a no deal are likely to support it," Gardiner told Sky News.

Asked if Labour was having conversations with those lawmakers, Gardiner said "Of course". (Reporting by Kylie MacLellan Editing by Keith Weir)