David Cameron's plan to hold an in/out referendum on the UK's membership of the EU has cleared its first hurdle in the Lords.

Peers gave the European Union Referendum Bill an unopposed second reading after a marathon debate involving more than 50 speakers.

But the Opposition served notice that it will try to amend the legislation, particularly on extending the vote to 16- and 17-year-olds.

Labour plans to put down an amendment tomorrow, which is likely to attract backing from the Liberal Democrats and could lead to a defeat for the Government in the Bill's later stages.

Foreign Office minister Baroness Anelay of St Johns ruled out extending the franchise to 16- and 17-year-olds, insisting the legislation was not the right "vehicle" for doing this

And she dismissed calls for EU citizens resident in the UK to be given the chance to take part, telling peers: "Many of the British public would view the inclusion of EU citizens as a crude attempt to fix the result."

The legislation has already cleared the Commons, where the Prime Minister suffered an embarrassing defeat over purdah rules ahead of the poll in a Tory backbench rebellion.

Lady Anelay pledged that the Government would not seek to overturn the vote it lost in the Commons.

With pro- and anti-EU membership groups having launched their campaigns ahead of months of gruelling debate, she promised a "fair and transparent" campaign.

Lady Anelay said Britain's relationship with the EU had changed "beyond all recognition" in the 40 years since the last poll on membership and it was right to give people a say now.

The Bill sets the end of 2017 as the deadline for holding a referendum but Lady Anelay indicated that progress on renegotiating membership terms will determine the final date.

"The negotiation will be difficult. There will be noise and possibly setbacks along the way.

"But the Government is confident it can negotiate a new deal to put to the British people at the referendum itself," she said.

The Government had a clear mandate to hold a referendum and would ensure a "fair campaign so that the deck is not stacked in favour of one outcome or the other".

Labour's foreign affairs spokeswoman Baroness Morgan of Ely accused the Government of "incredible naivety" in failing to set out what would happen if Britain pulled out of the EU.

"The British people have a right to know what their country will look and feel like if they vote to leave the EU."

Lady Morgan called for 16- and 17-year-olds to be given the vote, arguing it was inconsistent for them to be allowed to vote in Scottish and Welsh referendums, but not this one.

She said they deserved a referendum vote, adding: "We all remember the intelligence and enthusiasm with which the youngsters of Scotland engaged in the independence referendum."

Liberal Democrat spokeswoman Baroness Smith of Newnham backed calls for the franchise extension, saying: "This Bill is about the future of the United Kingdom but if it's about the future of anybody it's about our young people.

"The referendum last year in Scotland demonstrated that 16- and 17-year-olds can be trusted to vote, they can be trusted to engage in political decisions and these are questions about their future ..."

Tory former chancellor Lord Lawson of Blaby made a passionate plea for Britain to abandon the EU project and "embrace a global future".

Lord Lawson warned: "I have no doubt that overall the EU economically does more harm than good."

He dismissed as "tosh" suggestions that by leaving the EU the UK would still be bound by EU regulations but no longer have influence on them.

Insisting that the UK would be able to negotiate a free trade agreement with the EU, Lord Lawson said: "Let's not be afraid. We will have a whole lot of scare stories. Let's not be little Europeans. Let our horizon be global.

"Future growth of the world economy is going to happen much more outside Europe.

"The time has come to rediscover our national self-confidence, to abandon a political project which we don't share and embrace a global future."

But Labour's Lord Liddle warned that to vote to leave the EU would be final. "We will be on our own with no way back."

Tory former chancellor Lord Lamont of Lerwick said Britain could "survive perfectly well" outside the EU.

He told peers: "My position on the referendum is that I will wait and want to see the results of the renegotiation before I finally make up my mind.

"A renegotiated settlement for Britain which changed our relationship significantly would have much to commend it."

Baroness Royall of Blaisdon, former Labour leader in the Lords, hailed the referendum as "the most significant vote of my lifetime with huge implications for the future of Britain".

Backing the call for 16- and 17-year-olds to be given the right to vote, she said: "The referendum is important for my generation but much more so for the young people of our country, my children and my grandchildren. This is about their future."

Ukip's Lord Willoughby de Broke mocked the Prime Minister's "sadly unambitious wish-list" for change.

"There is an increasing groundswell in the country that the EU game isn't worth the candle and we would be better off out," he said.