The government faces a potential revolt in both houses of parliament over its refusal to let 16- and 17-year-olds take part in a referendum on EU membership, amid growing concern over how the vote is to be conducted.

Tory MP and former minister Sir Peter Bottomley, a long-term supporter of voting at 16, has signed a Commons motion backing an extension of the franchise and said he believes other Conservative MPs will follow suit.

Meanwhile, peers are planning amendments to the referendum bill in the Lords in hope of embarrassing the Commons into backing voting from 16, which was allowed in last year’s referendum on Scottish independence. Under current plans only those aged 18 and over will have a vote in the EU referendum, to be held by the end of 2017.

A leading pro-European peer said there would be “overwhelming backing in the Lords” for votes from 16 because Labour, Lib Dem and crossbench peers, most of whom like the idea, have a comfortable majority over the Tories.

While the Lords will not seek to force their will on the Commons – because the referendum was a key part of the Tory manifesto – it seems determined to force ministers to explain why they do not plan to give 16- and 17-year-olds a say.

Bottomley said he’d been impressed with the work of the youth parliament and youth councils, and letting teenagers vote in the referendum would be a way to increase political engagement.

Meanwhile, senior figures at Westminster are calling on ministers to give details before the referendum on the UK’s options if it votes to leave the EU. Lord (Gus) O’Donnell, the former cabinet secretary, told the Observer ministers need to be clearer with the public about what life outside the EU would entail, and whether the UK would seek a relationship similar to that of Norway, which is a member of the single market but has no say in its rules. He also called for the government to commission and publish more work on the economic consequences of quitting the EU.