Foreign Secretary William Hague says core sanctions on Iran will remain in place. These include sanctions against the Iranian Central Bank, US trade restrictions, all UN Security Council sanctions and restricted access to its foreign assets.
Most importantly, the EU ban on Iran's crude oil will also remain in place. For Iran, this means loss of sales worth about $4 billion (£2.5 billion) per month.
When you consider the diplomatic mountain the US and Iran have already scaled, you get a daunting sense of the challenge ahead.
The deal between Iran and world powers looks like a breakthrough, but with six months of wrangling over details ahead, it could still fail.
The nuclear agreement between Western powers and Iran was broadly welcomed by politicians, former world leaders and Middle East experts.