LONDON—The United States and the U.K. dismissed reports coming out of Iran that they are thrashing out a prisoner exchange deal with Tehran that could see the imminent release of a British-Iranian woman, Nazanin Zaghari-Ratcliffe, and four Americans, among others. Iran was a key topic of discussions Monday between U.S. Secretary of State Antony Blinken and his host in London, British Foreign Secretary Dominic Raab. Their meeting took place a day before the first face-to-face meeting of foreign ministers from the Group of Seven leading industrial nations in two years, largely due to the coronavirus pandemic. Iran, Ukraine, China, Russia, climate change and COVD-19 are expected to dominate the talks. Blinken’s visit to London, his first since being appointed by President Joe Biden, comes amid mounting speculation of a prisoner swap deal with Iran. Such exchanges are not uncommon and were a feature of the 2015 nuclear accord between Iran …