He said a plain reading of law makes it clear that for a person to be recognised for the post should be leader of a party in Opposition with the greatest numerical strength.
He was rejecting suggestions that Congress, with 44 MPs in the Lok Sabha, may not get the post of Leader of the Opposition.
"Beyond these legal requirements mentioned in Section 2 of The Salary and Allowances of Leaders of Opposition in Parliament Act, 1977, there appears to be no other condition such as the minimum number of strength of such party equivalent to the quorum of the house," Moily said in a statement to PTI.
He said the "ambiguity" on the issue has arisen due to the practice being followed by the Lok Sabha Speaker in granting recognition to Leaders of the Opposition in the past.
"The practice has been to read Direction 121 of the Directions of the Speaker which says that in recognising a Parliamentary Party or Group, the Speaker should ensure that it shall have at least a strength equal to the quorum fixed to constitute a sitting of the House, that is one-tenth of the total number of members of the House.
"Thus by a combined reading of Direction 121 and Section 2 of the Act, the practice of insisting the minimum requirement of 55 members has evolved. In this context it may be mentioned that directions of the Speaker cannot override a statutory requirement," he insisted.
Moily said the proponents of this view have adduced another provision in the Leaders and Chief Whips of Recognised Parties and Groups in Parliament (Facilities) Act, 1998 to justify the condition that for Leader of Opposition a party must have a minimum of 55 members.
"Section 2 (b) of the Act defines recognised party for a different purpose -- for grant of certain facilities for Chief Whips. The said section defines recognised party as a party, which has a strength of not less than 55 members in the House. However this argument is fallacious since the object of the two Acts are totally different and the prerequisite of on Act cannot be read into another Act to curtail its scope," he said.
According to Moily, Parliament cannot function without a Leader of Opposition since then many provisions in the Acts of Parliament have recognised and have assigned a definite role for the Leader of Opposition in appointments to statutory bodies and authorities.
Congress spokesperson Abhishek Singhvi, also a senior lawyer, said there is a difference between statutory requirements for availing of prerequisite or being the Opposition leader.
"Certainly statutory preconditions have to be satisfied. But there is absolutely no legal bar over the discretion of the Speaker to recognise in functional terms of group, leader or party as Opposition," he said.
Congress could have Leader of the Opposition if the Speaker relaxes the rules or recognises the entire UPA as a block, which has 56 MPs.
Congress got 44 seats in the Lower House this time and to be recognised as the main Opposition, a party has to get at least 10 per cent of the total strength of the 543-member House - that is 55 MPs.
However, there is nothing statutory about this requirement, which can be waived by the Speaker.
There is also speculation that AIADMK and Trinamool Congress having 37 and 34 members respectively can come together to claim the post.