MPs rejected the idea by 303 to 253 on Tuesday, overturning an amendment to the EU referendum bill passed in the House of Lords that would have lowered the voting age to 16.
But Labour sources said peers were refusing to accept the decision of the House of Commons in a development that is set to lead to a dramatic standoff between the two chambers next week.
The government is growing increasingly frustrated with the Lords, which has defeated it on numerous occasions since May – including the blocking of the Treasury’s plans to cut tax credits in October – because there are more Labour and Liberal Democrat peers than Conservatives.
Ministers are seeking to curb its powers to block secondary legislation in a new inquiry led by Lord Strathclyde, but peers are still able to use parliamentary procedure to delay and frustrate the government’s aims.
In an attempt to see off the proposal for votes at 16, the government declared there was little public support for such a move and it would have looked like an attempt to rig the contest.
The fact that lowering the voting age would incur costs of about £6m meant that the Speaker could rule it to be a “financial” measure and therefore exempt from further interference from peers.
Labour is refusing to back down, however. The next step will be for peers to table a similar but different amendment, while keeping the same aim of extending the franchise for the EU referendum.
The Lords is likely to debate any such amendment on Monday, before batting the legislation back to the Commons, possibly on the same day, in a parliamentary process known as ping-pong.
It will be a race for the government to get the issue resolved before parliament breaks up for Christmas because it wants the bill on the statute book as soon as possible.
One Labour aide described it as a “game of chicken” and even suggested that an obscure parliamentary procedure called “double insistence” may be invoked that could end in the whole EU referendum bill being killed off.
However, another senior Labour source said this was not possible and peers would instead simply send the Commons another amendment with different wording but with the same intention and no financial implications.
Labour is strongly disputing the idea that the bill really has financial implications, as the sums involved are small in the context of the overall budget and millions of pounds would have to be spent anyway on identifying 16- and 17-year-olds who will be eligible to vote by 2020.
Downing Street sources confirmed they were expecting a parliamentary tug of war over the legislation.
During the debate, John Penrose, a Cabinet Office minister, told MPs it would be wrong to change the “tried and tested” general election voting age for a single poll.
“This is not some great progressive cause where an oppressed minority is waiting to be liberated by enlightened public support, quite the opposite in fact,” he said.
“The risk is that for those watching our debate outside this chamber, it will seem like a Westminster bubble issue. A trendy obsession for an out-of-touch political class rather than a burning social crusade with widespread democratic support.
“Even worse, there may be a suspicion that some are supporting this motion because they feel they could gain some tawdry tactical party political advantage from it for one side or the other.”
However, Pat McFadden, the shadow Europe minister, said such a major constitutional referendum was a “once-in-a-generation choice, perhaps a once-in-a-lifetime choice” about the future of the country.
“Our contention is very simple, it is that the young people of this country deserve a say in the decision which will chart our country’s future,” he said.
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