Ecuador's ambassador to the UK, Ana Alban, has told ITV News the microphone allegedly found inside her embassy is going to be sent away to be tested.
She said: "We found something, but we don't know what it is, and we are sending it to someone...I don't know how long it has been there."
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Tory Eurosceptic Jacob Rees-Mogg played down the significance of the deal struck by the Government to win over pro-EU rebels.
The Tanaiste issued the warning to the UK ahead of a visit to Dublin by European Commission President Jean-Claude Juncker.
Around 9,500 people gathered at the neolithic World Heritage Site to attend the overnight celebration of the longest day of the year.