As the British Government demand answers from Russian president Vladimir Putin over the incident, Rhondda MP Chris Bryant fiercely criticised Mourinho.
Prime Minister May has said the United Kingdom must "stand ready" to take action against Russian Federation and that this would be set out in the Commons on Wednesday should there be no adequate explanation from the Kremlin by midnight on Tuesday.
Bryant's fellow Welsh Labour MP Stephen Doughty urged Mourinho to reconsider his position.
"RT has repeatedly conned viewers with a veneer of respectability, while taking its orders from the Kremlin".
Media in the United Kingdom, which could never forgive Russian Federation for its clean victory to host the FIFA World Cup over London, are the most active players in the calls to boycott the global competition, the press release added.
The English Football Association, whose president is Prince William, has avoided commenting directly on calls by some politicians, including the leader of the Liberal Democrats, not to send its national team to Russian Federation.
The British government made the accusation against Russian Federation for its alleged implication in Sergei Skripal's case, as a provocation and an effort to start a media campaign to discredit this country as the host of the FIFA World Cup, the Foreign Ministry said in a communiqué.
Now in its second week, the controversy started when former spy Sergei Skripal and his daughter Yulia fell seriously ill in Salisbury on March 4.
Broadcasting regulator Ofcom issued a statement on Tuesday, following Prime Minister Theresa May's update on the investigation to parliament on Monday, and said it would wait for her next public comments on Wednesday before considering "the implications for RT's broadcast licences".