"Britain opposes boycotts," he said.
"Whether it is trade unions campaigning for the exclusion of Israelis or universities trying to stifle academic exchange, Israel's place as a homeland for the Jewish people will never rest on hollow resolutions passed by amateur politicians," Cameron said.
"Delegitimising the State of Israel is wrong. It's abhorrent. And together we will defeat it," he added.
Cameron held talks in Jerusalem with Prime Minister Benjamin Netanyahu soon after his arrival earlier today on the two-day visit to Israel and the Palestinian territories to discuss the Middle East peace process and Iran's controversial nuclear programme.
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Cameron's visit comes as the US-led peace negotiations struggle to make headway before an April 29 deadline, with US Secretary of State John Kerry pushing both leaders to accept a framework proposal that would extend the talks to the year's end.
Netanyahu stressed joint "security challenges" facing the international community, in his meeting with Cameron.
"We have political and security challenges that we want to achieve in cooperation with one another," Netanyahu said, according to a statement from his office.
Netanyahu was also to impress on Cameron on the need for Europe to push the Palestinians "to change their current behaviour" in the peace talks, the Jerusalem Post newspaper said.
Israel has blamed Palestinian "intransigence" for blocking progress in the negotiations.