Boris Johnson has rejected calls to take disciplinary action against the Israeli embassy in London after one of its officials was caught on camera in an undercover sting plotting to “take down” UK MPs regarded as hostile, including the foreign office minister Sir Alan Duncan, who is an outspoken supporter of a Palestinian state.

Speaking in the Commons on Tuesday, the British foreign secretary said the diplomat Shai Masot was no longer working in London, and that the Israeli embassy had issued a very full apology so he considered the matter closed.

Conservative MPs including Hugo Swire challenged Johnson to explain why the British ambassador to Israel had been formally summoned when the UK backed a UN resolution condemning illegal Israeli settlements, but no comparable action had been taken when an Israeli embassy employee “is caught on film conspiring with a civil servant to take down a senior minister in his own department, the chairman of the foreign affairs select committee and other members of this house”.

Swire asked for the thinking behind the UK’s decision to forgive and forget the incident on the basis that the Israeli ambassador “makes a couple of phone calls” .

Johnson replied: “The Israeli ambassador made a very full apology for what had taken place and the diplomat in question seems no longer to be a functionary of the embassy in London – so whatever he may exactly have been doing here his cover may well be said to have been and well truly blown – so the matter can be considered closed.”

Alex Salmond, the former Scottish first minister, said that if a UK diplomat were caught making such threats in Tel Aviv they would be booted out.

Johnson also defended the UK’s decision to support the UN resolution condemning the Israeli settlements, saying the 20% extra settlements since 2009 were a threat to peace. He said the UK had been closely involved in drafting the language of the resolution, ensuring it contained words condemning “the infamy of terrorism that Israel suffered every day”.

He said it was too early to say exactly what the Trump administration’s policy on illegal settlements would become, but he promised the UK would continue to make its position clear.

He said it was a widespread view in Washington and across the UN security council that the Israeli settlements were illegal.