The claim came as Mr Baker, now a backbencher, challenged a ruling that he had been in contempt of court when he ignored a High Court order to bring an asylum seeker back to Britain.
The case, described by acedemics as the most significant constitutional hearing for two centuries, centres on Mr Baker's argument that he enjoyed immunity from 'coercion' as Home Secretary. He says members of the Government only lose this immunity if they deliberately set out to flout judicial authority.
However, Sydney Kentridge QC, for the asylum seeker, told the Law Lords: 'The whole point about the law of England is that once you do a wrong, it matters not whether you are doing so for a private purpose or in the authority of the Crown. If it's a wrong, you are liable and you cannot say 'I was doing it in my official capacity'.'
The case began when the asylum seeker, known for his safety as 'M', arrived in England from Zaire almost three years ago.
His claim for refugee status was rejected by the Home Office, but his solicitors appealed to the High Court to stop the deportation. However, as a result of a breakdown in communication, M was returned to Kinshasa before the appeal could be heard, prompting Mr Justice Garland to order that he be brought back to Britain the following day.
Mr Baker, advised that the judge was wrong to make such an order, decided to ignore it. Although the order was later overturned, the Court of Appeal said the former Home Secretary had no right to do so, finding that he was in contempt.