The government has been urged to end the 41-year-old ban on the tapping of MPs' telephones by the secret services.
Tony Blair considered ending the ban on phone-tapping last year
Sir Swinton Thomas, the outgoing Interception of Communications Commissioner, said no one should be considered "above the law".
Former prime minister Harold Wilson introduced a ban on phone-tapping MPs in 1966. Supporters say this allows them to do their job "without fear".
But Sir Swinton said MPs backed the ban out of "self-interest".
The intelligence community was undermined by the rule, known as the Wilson Doctrine, he added.
In a report to Parliament, he said: "It is fundamental to the constitution of this country that no-one is above the law or is seen to be above the law.
"But in this instance, MPs and peers are anything but equal with the rest of the citizens of this country and are above the law."
Mr Blair re-considered the Wilson Doctrine last year after revealing that Sir Swinton had called for an end to it.
But he subsequently rejected the advice, telling the Commons he had pondered it "very seriously".
In his report, Sir Swinton said he understood Mr Blair's decision, but added: "What is more difficult to understand is the basis of opposition apart from self-interest or, possibly, lack of understanding, in the maintenance of a privilege enjoyed by nobody else, given that there are perfectly adequate safeguards in place that serve MPs and non-MPs alike.
"In the conversations that I have had with ministers and Members of Parliament on this issue, I have not been able to find any logical, and, certainly not, any principled objection to change apart from self-interest."
Those in legal and intelligence circles had shown "astonishment and incredulity that this situation should be allowed to continue", he added.
Sir Swinton said he was aware of no other country in the world with similar arrangements, which did not apply to members of the European Parliament, the Scottish Parliament or the Welsh or Northern Ireland Assemblies.
"In my view the doctrine flies in the face of our constitution and is wrong," he added.
"I do not think it provides MPs with additional protection. I think in fact it is damaging to them."
Sir Swinton, who was responsible for overseeing the way police and spies carry out intercepts, officially left office last April.
But he has continued to work alongside his successor, Sir Paul Kennedy, to prepare the report covering the last 15 months of his tenure.
The report is his last before he relinquishes his duties.
The Wilson Doctrine was introduced to prevent the tapping of phones belonging to MPs.
But it was subsequently widened to cover all forms of communication, including electronic eavesdropping, and to protect members of the House of Lords.
Last year, Labour MP and former defence minister Peter Kilfoyle said ending the ban would make it harder to "hold the government to account".
Lib Dem Simon Hughes said MPs should be exempt from phone-tapping so they could question ministers "without fear".