Lawyers and justice groups claim he is being denied suitably experienced barristers to represent him at the forthcoming appeal against his conviction for the contract killing of Corinne Bentley, 22, at a remote Manx farm a year ago.
Teare, 19, convicted in July, is apparently hoping to call new evidence at the appeal.
Peter Thornton QC, and Anthony Burton, two leading criminal lawyers from England, are prepared to offer their services free. But they have been refused the necessary licence by the island's governor, Sir Laurence Jones. Instead, Teare has been offered a lawyer from the Manx Bar.
With the island's relatively low crime rate - the last murder was over 10 years ago - legal groups, lawyers and Teare's family believe none have the experience to deal with such a serious case. Tax, company law, probate, matrimonial and conveyancing are the more usual fields of expertise on the Isle of Man.
Justice, the British section of the International Commission of Jurists, has written to Kenneth Clarke, the Home Secretary, expressing its concern at the governor's ruling, taken after discussion with the local judiciary.
Sir William Goodhart QC, writing on behalf of Justice, told Mr Clarke that, normally, lack of expertise on the island is overcome by the granting of a licence to English lawyers. It was done, for example during recent fraud trials resulting from the collapse of Savings and Investment Bank.
Sir William said: 'It seems anomalous that in a murder appeal, carrying the penalty of death for a 19-year-old boy, different considerations appear to apply.'
Yesterday a Home Office spokeswoman said that the letter was receiving urgent consideration.
But in the Isle of Man, the government defended its action.
Fred Kissack, government Chief Secretary, said: 'The seriousness of the offence is not one of the criteria for the granting of a licence. It would be demeaning of the Manx legal profession to suggest every time that there is a serious crime that they are not capable of dealing with it.'
Teare's death penalty - even if upheld by the appeal judges - will be commuted by the Home Secretary, in the same way as two others in the last 20 years. A new Bill to be introduced this autumn in the Manx parliament will abolish the penalty, bringing it into line with the rest of the British Isles.
Teare was convicted of the killing of Ms Bentley largely as a result of a disputed confession - taken in the absence of a lawyer - in which he was said to have commented that pounds 600 was too little for the job. His lawyers argued then that there was no forensic science evidence linking him to the killing.
Anne Owers, director of Justice, said yesterday: 'Although we cannot yet form a view on his protestations of innocence, there are concerns about the evidence, and he should clearly be able to have the best possible representation on such a serious charge.'