Major told the BBC the "poison needs to be let out of the system."
The British government has refused to release full details, although an overall summary has been made public.
Major said it would benefit Prime Minister Tony Blair to release the advice by Lord Goldsmith.
"I cannot see any credible or logical reason why -- given the circumstances as they now are, given the fact that they have already published a summary of the opinion, given the fact that there is no doubt Lord Goldsmith produced such an opinion -- I cannot see at all why that should not now be published," Major told the BBC Sunday.
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