The government has come under fire for failing to consider reform of the House of Lords in a wider constitutional context.

Charter 88 warned the government on Monday that it "makes little sense" to proceed with reform of the upper house without considering parliament as a whole, its relationship with the executive, devolution and changes to the legal system.

Giving its response to the government's white paper on reform of the House of Lords, the constitutional reform group has called for peers to be replaced with a directly-elected Senate with broadly the same powers as the present house.

While ministers have hinted at some flexibility in their plans for reform of the Lords, Charter 88 is calling for a chamber made up of 261 or 348 directly elected members, elected via large multi-member regional constituencies using the European parliament boundaries.

The group believes that elections should be held using single transferable vote system, and members of the house would be allowed to stand for a single 10 or 12-year term only.

The campaigners put forward a selection of election timetables, with either a third of members being elected in each region every four years on the date of fixed-term general elections, or elections held on the same cycle as elections to the devolved parliament and assemblies, or with half of the members being elected every five years on European parliament election day.

The proposals would see the reformed Lords retaining its primary function as a revising chamber, but with the law lords removed to form a separate Supreme Court and an end to the Church of England's privileged position. Members of the Senate would be given a new role in scrutinising public appointments.

Charter 88 says there is no need for any radical changes to the powers of the upper house, with the retention of its one year delaying power over primary legislation and power of veto over secondary legislation. But there is support for a new power to amend secondary legislation.

Existing life peers should be offered a retirement package based on their recent attendance record, with their numbers being phased out as each tranche of elected members is introduced, the submission argues.

While the Lord Chancellor, Lord Irvine of Lairg, argued last week that the number of elected peers should remain "substantially" below 50 per cent to prevent the upper chamber challenging the legitimacy of the Commons, Charter 88 puts forward an alternative solution.

"Government ministers should not sit in the Senate. Confining government ministers to the Commons would help to distinguish the two chambers, secure a degree of independence for the Senate and emphasise the superiority of the Commons," says the report.

And Charter 88 repeats the view, shared by many Labour backbenchers, that the government is failing to overhaul the "unacceptable" system of patronage to the upper house.

"The government has not attempted to justify composing the second chamber of 55 per cent party political appointees. Patronage exercised by the prime minister and other party leaders is not an acceptable method of filling one half of our legislature."