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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After a mild start temperatures should pick up, with the south of England seeing highs of 26C.
In Edinburgh tonight you can hear it and feel it. The buzz, the banter of the day and the thrilling sense something big is coming tomorrow.
There is nervousness, anxiety and on the streets of Edinburgh fuelled by an atmosphere unlike anything seen before in recent UK politics.