A KEY reason for leaving the European Union was to restore parliamentary sovereignty. So it is ironic that this week’s debate over the EU withdrawal bill, formerly known as the Great Repeal Bill, should centre on claims that the executive is usurping parliamentary powers—even more so since David Davis, the Brexit secretary, for years fought hard against such government encroachment.

Nobody disputes that the bill is needed. It gives effect to Brexit by repealing the 1972 European Communities Act. To provide continuity it also translates into British law 12,000-odd EU regulations written in the past 45 years. The big argument is over how to do this. MPs have raised two main issues. The first is the bill’s use of secondary legislation to amend laws by ministerial fiat without parliamentary scrutiny. The second is the question of Parliament’s role in overseeing Brexit.

Secondary legislation has long been a matter of constitutional concern. The Hansard Society, a parliamentary research group, and the House of Lords have both criticised the present system. Too many statutory instruments are waved through unscrutinised or even unread. The new bill makes this worse by giving ministers extensive powers to propose secondary legislation whenever they deem it appropriate.

The government says it will use these powers only for technical changes. Yet clauses seven to nine of the bill are extremely broad. They let ministers change primary legislation wholesale, using so-called Henry VIII powers (after that king’s rule by decree), and spend money. They put the burden of proof on those saying these powers are being misused. Even many Tory MPs want to limit the clauses’ scope. Some suggest the two chambers should form a joint committee to scrutinise Brexit-related statutory instruments.

The case for broader parliamentary oversight is strong. But Commons select committees, which play an important scrutinising role, have not been set up since the election on June 8th. Mr Davis also rejected requests by the House of Lords EU committee to appear in August or September. He has promised a parliamentary vote on a Brexit deal, but many MPs say this means little, since rejection could mean leaving the EU with no deal at all.

Although the Labour opposition will vote against the second reading of the withdrawal bill on September 11th, it is expected to pass. But it faces amendment at a later stage. Efforts to deter Tory rebels by accusing them of blocking Brexit or threatening another election that might put Jeremy Corbyn in power convince few. Even if MPs yield to the party whips, the Lords (where the government has no majority) will not, so the withdrawal bill seems sure to be weakened. It is another irony that unelected peers may do more to shape Brexit than elected MPs.

That will also become clearer in other Brexit-related laws this autumn. The response to a leaked draft of the government’s tough new regime for EU migrants suggests opposition to the government’s “hard” Brexit is strong. So does broad support for a transitional period that retains most current EU arrangements after March 2019, the scheduled date for Brexit. Mr Davis has been having a torrid time negotiating in Brussels; he may find that life in Westminster can be almost as trying.