The Institute for Fiscal studies has estimated that abolishing the cap could lift more than 600,000 children out of poverty across the UK at a cost of about £3.6bn a year.
Laura Dunn, a former adviser to Conservative Prime Minister Theresa May and now a political consultant, believes the cap should stay to limit increasing welfare costs.
She said “there are only two ways” for the UK government to fund lifting the cap “extra borrowing or tax increases”.
She also suggested it would be unfair to ask families who refrain from having more children because of affordability to subsidise others.
“If people are expected to cut their cloth according to their own finances,” she said many would question why they should be “paying for others who are not prepared to do the same”.
Eluned Morgan repeated her call for the cap to be scrapped, in First Minister’s Questions on Tuesday, saying she also wanted “more money for public services and support with the cost-of-living crisis” in Rachel Reeves’ budget.
Welsh Conservative Senedd leader Millar accused her of rattling off “a few small ticket items” rather than “shouting from the rooftops” demands, as he said Welsh Labour had done when Tory ministers had held power at Westminster.
Plaid Cymru leader Rhun ap Iorwerth told Morgan his party’s demands included reclassifying “unfair spending decisions that deny Wales billions” and unlocking “Wales’ borrowing powers to address historic underinvestment”.