Legalising gay marriage would not lead to schools having to amend textbooks as some MPs have suggested, but would rather bring laws in line with existing school rules, the Malta Gay Rights Movement has said.

"The MPs concerned seem to be forgetting that Maltese law and public policy has already changed where the recognition of Rainbow Families is concerned," the MGRM said, noting that schools were already required to recognise diverse sexual orientations and gender identities in their practices.

"There is no heterosexist, homophobic or transphobic bubble big enough to somehow isolate children from the world around them," it said.

The MGRM statement comes one day after The Sunday Times of Malta reported that some disgruntled Nationalist Party MPs are not happy about the party cracking the whip and instead want a free vote on the issue.

Parliament is set to debate the bill during its opening session later today and Prime Minister Joseph Muscat has said that he would like to see the bill passed into law before MPs take their summer recess.

In its statement, the MGRM also argued that other concerns raised about the bill were misguided.

Using gender neutral terms was the "simplest and most logical solution" to a system which recognised the diverse gender combinations possible for a married couple, the lobby group said, and would remove anomalies that could arise from current legislation.

Likewise, concerns that the draft bill sought to preempt changes to the Embryo Protection Act were ill-founded, the group argued. Gay couples could already access reproductive or surrogacy services overseas to have a child, and the legal changes proposed would ensure that children's parents would be legally recognised "irrespective of the biological ties that may or may not exist."

"If ‘improvements’ to the proposed bill means addressing any oversights they are certainly welcome," the MGRM concluded. "If however it means compromising on inclusion to maintain heterosexual and cisgender privilege, then no thank you."