Eighty-eight MPs have now backed a move to force transparency measures on Britain's Crown dependencies.
When initially tabled, the amendment to the UK's Financial Services Bill was backed by 42 MPs.
The move by former Tory Chief Whip Andrew Mitchell and Labour's Margaret Hodge seeks to make the ultimate owners of island companies public.
The move is being resisted by Jersey, Guernsey and the Isle of Man governments, who say it is unconstitutional.
They also argue they keep accurate company information and are doing enough to tackle financial crime.
Labour MPs make up the bulk of the 88 backing the amendment, but the move also has the support of 24 Conservatives.
They include former Tory Cabinet ministers Ken Clarke, David Davis and Sir Oliver Letwin.