It happened in Egypt during the Arab Spring, when Israeli diplomatic staff were the first to leave Cairo. It happened in Libya in July 2011*. It happened in Iraq in 2003 just prior to invasion.
Why is this relevant today?
UK Foreign Office says 'to ensure their ongoing safety, some staff are leaving Tehran' embassy.
* or maybe that didn't happen, which is in itself even more compelling... please correct or enhance this post, there's every chance it's total bullshit and scaremongering (just like the mainstream (corporate war) media, one could say) if you leave it to me to DO EVERYTHING FOR YOU.