Danny Alexander, the most senior Scottish member of the cabinet, will on Wednesday “read the riot act” over what he claims are confusing Tory messages which allowed Alex Salmond to claim that David Cameron was reneging on his pledge to devolve further powers to the Scottish parliament.

The Liberal Democrat chief secretary to the Treasury will use the first meeting of a new cabinet committee, which is meant to draw up plans to protect the rights of MPs beyond Scotland, to say that the Tories caused immense damage north of the border.

William Hague, the leader of the House of Commons, will chair the first meeting of the cabinet committee which was set up by David Cameron to provide an answer to the West Lothian question – the anomaly whereby Scottish MPs are able to vote on English-only matters while MPs from south of the border have no say over devolved matters such as health and education at Holyrood.

The prime minister caused alarm in Labour and Lib Dem circles when he announced in Downing Street early on Friday morning, shortly after the declaration of the result in the Scottish referendum, that the devolution of further powers to Holyrood must move “in tandem with, and at the same pace as” addressing the West Lothian question. Michael Gove, the Scottish-born Tory chief whip, angered Alexander when he said on Saturday that it would be “impossible” to introduce one reform without the other.

Alexander will tell his colleagues that the mixed messages had provided a gift to Salmond. He told the Guardian: “The success of the referendum campaign was the clear agreement from all the party leaders to deliver change to Scotland in the event of a no vote. The way that those commitments were wrongly called into question over the weekend has been damaging in Scotland. It is absolutely essential that we stick to what was agreed – no ifs, no buts – and there is no repeat of the harmful messages of last weekend.”

Hague will tell the cabinet committee that the Tories have made an unequivocal commitment to deliver the extra powers to the Scottish parliament that are to be drawn up by a committee chaired by the cross-bench peer Lord Smith of Kelvin, who was praised by Salmond in the Scottish parliament on Monday. But the leader of the Commons will also say that the Tories are determined to change voting rules at Westminster to deliver “English votes for English laws”.

A meeting of Tory MPs at Chequers on Monday, chaired by the prime minister, agreed that proposals by the former Commons clerk Sir William McKay are a good starting point. McKay proposed a “double majority” voting system at Westminster to ensure that legislation relating to England secures the support of a majority of English MPs and MPs across the UK.

Alexander told the Guardian earlier in the week that it was important to achieve political consensus. Labour has said that English-only votes should be examined in a constitutional convention that should be set up after next year’s general election.

The Lib Dem cabinet minister will also say that the strong engagement of 16- and 17-year-old voters in the referendum showed that this age group should be allowed to vote in next year’s UK general election. Ed Miliband voiced support for this idea in his Labour conference speech.