The Government's plans to give English MPs an effective veto over Westminster legislation have been criticised by a cross-party committee.
The Procedure Committee branded some of the proposals "over-engineered and potentially burdensome", and insisted they should be piloted before being introduced fully.
The changes, known as English votes for English laws, or Evel, would introduce a new parliamentary stage for laws that do not affect other parts of the UK.
English or English and Welsh MPs would scrutinise such legislation alone and then accept or veto it before a final reading in front of the whole House.
Ministers have argued that the system is the best way to address the so-called West Lothian Question as devolution progresses, but critics warn that it could create two classes of MP.
Procedure Committee chairman Charles Walker said: "Our initial review on these major proposals for change found that elements of the proposed procedures were over-engineered and potentially burdensome on the House.
"The committee has recommended changes which will give the whole House a say in how it applies these procedures, and will streamline the process required to allow colleagues from constituencies in England or England and Wales to vote on legislation which affects those constituencies only.
"Clearly the proposals represent a substantial change to the House's procedures, and they ought to be piloted on statutory instruments, and a small number of Bills, before they are fully implemented."
The committee supported the plan to change procedures by revising the Commons Standing Orders rather then bringing forward primary legislation.
They argued that the Speaker should be given "discretion" over which Bills he certifies as only affecting England or England and Wales.
"Committee members thought that he should not give reasons for certification decisions to the House, but that he should be left to use his discretion as to how best to discharge the requirements," Mr Walker said.
"Legal challenges to the decisions of the Speaker and to the procedures of the House, though unlikely to succeed, cannot be ruled out.
"It is important that legislation be drafted as clearly as possible to meet the tests for certifying England-only legislation."
Mr Walker said all members of the committee had made a "positive and collaborative contribution" to preparing the interim report.
"However, at the substantive vote to adopt the report as a committee report to the House, we were unable to secure the endorsement of the two committee members from the Scottish National Party," he added.
The SNP's Westminster leader Angus Robertson said: ''This report shows the utter confusion and total inadequacy of what the UK Government is proposing on Evel.
"The Tories have got themselves into a first class muddle and are trying to force this through – with too many flaws - too quickly.
"English Votes for English Laws puts forward an absurd solution to the UK's current constitutional inequalities and it is clear that the proposals need to go right back to the drawing board so that they can be examined properly."
Patricia Gibson, SNP member of the Procedure Committee, said: "Patrick Grady and I, the SNP members of the Committee could not sign up to the report since it fundamentally refused to recognise that the Commons is a UK parliament and that Evel effectively does not recognise this as it excludes MPs from areas outside England from voting on legislation that could have consequentials and effects on other parts of the UK."
Shadow Scottish Secretary Ian Murray said: "The Government's proposals for Evel are an incomprehensible mess.
"This report adds to the many expert voices who have already said that these proposals will not strengthen Parliament.
"Instead, David Cameron's proposals will weaken our democracy, weaken Scotland's voice in Parliament and for the first time create two classes of MPs.
"It could lead to the perverse situation where some unelected members of the House of Lords will be more powerful than elected MPs. Labour will put forward our own proposals that will simplify this process, but not threaten the way the UK's democracy works."
A Government spokesman said: "The Government is grateful to the Procedure Committee for their report, and we will respond before tabling our final proposals later this week.
"Our planned changes to the Standing Orders of the House deliver our commitment to introduce English votes for English laws. We are determined to strengthen the Union – we are devolving more powers across the United Kingdom to ensure a fair deal for every part of the country.
"The process will be reviewed after a year to ensure it is working effectively."