london british foreign minister boris johnson travel iran saturday lobby counterpart mohammad javad zarif release jail iranian-british aid worker nazanin zaghari-ratcliffe trip third british foreign minister iran last 14 years take place complex backdrop historical regional bilateral tensions johnson vow leave stone unturned britain efforts free zaghari-ratcliffe project manager thomson reuters foundation sentence five years prison convict iranian court plot overthrow clerical establishment deny charge foreign secretary urge iranians release dual nationals humanitarian ground foreign office spokesman say zaghari-ratcliffe dual national hold iran become high profile johnson say teach people journalism arrest april 2016 remark critics say could prompt iran extend sentence thomson reuters foundation charity organization independent thomson reuters operate independently reuters news say zaghari-ratcliffe holiday teach journalism iran johnson since apologize comment call resignation something threaten destabilize prime minister theresa may minority government crucial point britain brexit negotiations zaghari-ratcliffe tell appear court dec. 10 husband richard say visit sandwich meet oman unite arab emirates johnson key proponent britain exit european union take advantage gap domestic parliamentary calendar dominate brexit johnson surprise choice britain top diplomat appoint may 2016. record political gaffes use florid sometimes undiplomatic language visit test ability navigate political landscape litter potential pitfalls iran 1979 islamic revolution turn pariah state west many middle eastern neighbor international sanction recently lift part multilateral nuclear deal curb iran dispute uranium enrichment program deal threat u.s. president donald trump decide decertify iran compliance term agreement britain voice continue support nuclear deal one number western power voice concern tehran destabilize influence region visit come crucial time gulf region provide opportunity discuss peaceful solution conflict yemen future iran nuclear deal current volatility middle east spokesman say british foreign minister visit iran lobby jail aid worker