British fighters Shaun Pinner and Aiden Aslin spoke separately on the Rossiya 24 state TV channel, each being prompted by an unidenfied man.
It is not clear how freely the two men are able to talk in the footage.
Mr Pinner, 48, is a former Royal Anglian soldier. He was captured in Mariupol fighting alongside Ukrainian marines.
Mr Aslin, 28, from Nottinghamshire, had also been defending the beseiged city before being forced to surrender after he ran out of food and ammunition.
In the footage, both men ask Boris Johnson to help bring them home, in exchange for Ukraine release pro-Russian politican and oligarch Viktor Medvedchuk – known as the “Prince of Darkness.”