Claim of 'backdoor' lowering of voting age to 16
A row has broken out over claims that allowing 16 and 17-year-olds to vote on Scottish independence will lead to a lowering of the UK-wide voting age.
The government appears to have conceded that younger voters will have a say in whether Scotland remains in the UK.
One Labour MP said she hoped the "cultural shift" would lead to a lower age limit for UK general elections.
But Lord Forsyth, a Conservative, described the move as a "backdoor way" of forcing the hands of MPs.
Alex Salmond the Scottish First Minister will meet David Cameron next week to finalise a deal on how the 2014 referendum will be run.
Voters in Scotland are expected to be given a straight, in-or-out choice of whether or not to stay in the UK.
Mr Salmond has been pushing for 16 and 17-year olds to be able to vote in the poll.
Labour MP Natascha Engel told Radio 4's Today Programme: "The cultural shift that will come with allowing them to participate in the Scottish referendum will shift the mood in Westminster to make sure that 16 and 17-year-olds will be given the vote after that."
On Wednesday, government minister Lord Wallace said the coalition had no plans to extend the UK election franchise to younger people.
"The franchise for referendums is set out in the legislation that enables each referendum to take place," he said.
But Tory Lord Forsyth said if the law was to change it should be "properly debated by the House of Commons".
He accused Alex Salmond of "attempting to bully the prime minister" into lowering the age in return for having just a single question on any referendum ballot paper.
Constitutional expert Professor Vernon Bogdanor - a supporter of lowering the voting age from 18 - said "private negotiations" between David Cameron and Mr Salmond were "not the way" to bring about a change in the rules.
But he said such a change would make sense: "Sixteen-year-olds are still at school so they're having civics lessons and citizenship lessons so it's likely they'll pick up the habit of voting.
"By the age of 18 some people have left school so they've forgotten about their civics lessons and, as we know, the young on the whole don't vote very much."
According to pollsters Ipsos Mori, fewer than half of the 18-24 year olds registered to vote in the 2010 general election actually did vote. There was an almost even split in their support between the Conservatives, Labour and the Liberal Democrats.
And chief executive Ben Page suggested on BBC Radio 4's Today that allowing young people to vote might not benefit the SNP as the party hope.
"I'm not sure, if this is Alex Salmond's negotiation tactic, that it's going to pay off. In our most recent polling what we say is it's actually the 25 to 34-year-olds - who were teenagers when the movie Braveheart came out in the mid 1990s - who are actually most enthusiastic about independence in Scotland."