Election 2015: English only laws a 'dog's breakfast', says Jones
Labour First Minister Carwyn Jones has warned trying to bring in separate laws for England was a "dog's breakfast".
Mr Jones was responding to Conservative plans for "English votes for English laws", giving MPs for English seats a veto on issues only affecting England.
Mr Jones said it was difficult to argue against English laws "in principle", but in practice "it's difficult".
He repeated his call for a convention to be established to get a UK constitution with the "right balance".
On Friday, Prime Minister David Cameron said unless the current rules were changed: "English MPs will be unable to vote on the income tax paid by people in Aberdeen and Edinburgh, while Scottish MPs are able to vote on the tax you pay in Birmingham or Canterbury or Leeds.
"It is simply unfair. And with English votes for English laws we will put it right."
During election campaigning in Ammanford, Carmarthenshire, Mr Jones told BBC Wales such changes were not straightforward.
He said: "What is an English law? There is no English parliament.
"A Welsh law is a law that goes through the assembly, a Scottish law is a law that goes through the Scottish parliament.
"How do you know what an English law is? The problem is, it's an utter dogs breakfast, ok."
"At the moment, we have a situation where instead of, as I've suggested, everyone sitting down and saying 'right, let's plan this. Let's make sure we get a constitution for the UK that will work for the 21st Century, and let's get the balance right', it's all being done in bits and that's not going to work for the future."
Plaid Cymru's Jonathan Edwards said in principle his party was "in favour" of English votes for English laws.
"But for [the system] to work there must be equality of powers amongst the nations, else we risk a shambolic situation," he added.
The Liberal Democrats favour a grand committee of English MPs, with the right to veto legislation applying only to England, with its members based on the share of the vote.
The Welsh Labour leader also urged the "anti-Tory majority in Wales" to back Labour in May's general election, claiming up to 75% of voters wanted to defeat the Conservatives on 7 May.
A Welsh Conservatives spokesman called that message "desperate", accusing Mr Jones of relaying a "desperate message" when people were "sick of Labour taking Wales for granted."
Plaid Cymru said the first minister's claim that a vote for Labour was the only way to defeat the Conservatives was a "con" and Wales would get the best deal by "returning the strongest ever group of Plaid Cymru MPs".