Scottish Liberal Democrat leader Willie Rennie has accused the Conservatives of trying to rig the House of Commons to shore up their power in England.
Speaking at the launch of his party’s Scottish manifesto, Mr Rennie also urged people to “vote intelligently” to prevent the SNP getting a foothold in Westminster.
He said the Conservatives’ plans for English votes for English laws has been designed to solely benefit the Tories.
“We recognise that the constitution of the UK is evolving but you can’t do a timid reform that doesn’t embrace the necessary wider change,” he said.
“Most devolution that we have implemented in the UK has been a form of proportional representation, but what the Tories are doing are trying to rig it to just benefit them, so that Tories are in charge rather than the people.”
He said the Lib Dems have got a positive programme for Scotland and urged people to back it.
But questioned on whether people should vote tactically to keep the SNP out, he said: “In the 11 seats that we hold, it’s very clear that if you want to stop the SNP, the Liberal Democrats are best-placed to do that.
“People will use their vote intelligently throughout the country and I would encourage them to do so.”
He added: “We’re prepared to work with the SNP in other areas, and we have done so in councils and we have done it in the Scottish Parliament.
“But it would be unreasonable to put them in charge of an institution that they are against.
“You could just imagine Alex Salmond, deputy prime minister, and as soon as you have turned your back he’s got his screwdriver out trying to take the country apart.
“That’s not who you need in charge of the UK and we have said that is not reasonable.”
A key policy in the manifesto is a proposal to decriminalise the possession of drugs for personal use.
“If you look at Portugal, they’ve got a system of commissions so if someone is found in possession they need to go forward to the commission, and if the commission then decide that they need treatment then they are compelled to get that treatment,” he said.
“If they then fail to get that treatment programme then there are further penalties, but the first stint is going through rehabilitation.
“Too often people don’t get the proper rehabilitation in this country. That covers all drugs and it’s a very sensible way.
“But we need to be firm that people that are dealers will have the full force of the law brought down upon them.”