Berwick mp Alan Beith last night hit out at new laws that apply Scottish law to rivers flowing through the North-East countryside.
He complained the new legislation was badly drafted and "constitutionally objectionable".
But the Scotland Office insisted the change reflected 150 years of established practice.
Under the Scotland Act 1998 (River Tweed Order) 2006, expected to come into force later this year, parts of the River Tweed and its tributaries fall under Scottish fisheries law where they flow through England.
The reverse applies for the River Esk, whose Scottish stretches fall under English fisheries law.
Mr Beith argued the change went further than simply maintaining the pre-devolution state of affairs, as changes in Tweed regulations were previously subject to annulment by MPs at Westminster. But in future, a fisherman on the River Tweed or an English tributary, the River Till, could be prosecuted under a regulation made by a parliament where he was not represented, the MP argued. Mr Beith said: "The Scottish Parliament can change the law as it applies in England without England having any say at all. Scotland may have complained for years about England pushing Scotland around, but here's a case where England won't even have any say or any part in the debate."
But a Scotland Office spokesman said it was a sensible arrangement, just as the River Esk would be governed by English law. "It reflects the trust between the Government and the Scottish Executive and the UK and Scottish Parliaments that this legislation has given the Scottish ministers the right to make subordinate legislation.
"The Tweed Commission, who are responsible for the day-to day management of the river, contains a majority of representative commissioners appointed by local authorities, so there is democratic accountability on the governing body of the river."