Soleimanpour is allegedly connected to the 1994 bombing of a Jewish centre in Buenos Aires that killed 85 people.
Ambassador Morteza Sarmadi was recalled to Iran last week amid spiralling tensions over the arrest, at Argentina’s request, of the former Iranian envoy.
"Sarmadi came to Iran for consultations and he returned to Britain today (Sunday)," Foreign Ministry spokesman Hamid Reza Asefi told reporters.
Iran has said the case is politically motivated and Soleimanpour, who was envoy in Buenos Aires at the time of the bombing, has continued to protest his innocence.
Britain replied by saying its courts are independent of government.
Though Iran has cut ties with Argentina and warned Britain of “strong action,” analysts say that largely isolated Tehran is wary of prompting a response from other European Union states, at a time when it is under mounting pressure to allow tougher inspections of its nuclear programme.
Relations between Britain and Iran worsened last week when unknown assailants fired five bullets through windows in the upper storeys of the British embassy.