Iran will begin to freeze part of its nuclear programme in return for the sanctions relief from January 20.
The deal, agreed between Iran and world powers after months of negotiation led by the EU's foreign policy chief Catherine Ashton, is hinged on Iran curbing its enrichment of uranium.
Officials have another six months from January 20 to agree a final settlement about the activity the West suspects is aimed at obtaining nuclear weapons capability.
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David Cameron has addressed Parliament for the first time since Britain voted to leave the European Union.
The FTSE 100 Index fell to 2.55% to 5,982.2 at the closing bell as the financial markets continued to experience Brexit volatility.
Prime Minister David Cameron has called his Polish counterpart, Beata Szydło, to express concern over reported attacks on Polish migrants.