A bill allowing a referendum to be held on Britain's membership of the European Union has a 50/50 chance of making it through the House of Commons, the MP promoting it said.
Stockton South MP James Wharton is putting forward legislation drafted by the Conservative Party leadership, which would require a national referendum by the end of 2017.
Voters would be asked the question: ''Do you think that the United Kingdom should remain a member of the European Union?''
Prime Minister David Cameron has already pledged to do everything possible to bring the EU referendum bill to a vote - including by imposing a three-line whip on Tory MPs.
But Mr Wharton conceded the Bill's prospects appeared to be a " very close run thing".
He was quizzed on the chances of success when he appeared in a question and answer session at the Scottish Conservative Party conference in Stirling.
Mr Wharton said: "The second reading is on July 5, if it is successful it will depend partly on whether the Labour Party all turn up, we are hoping a few of the lazier Scottish MPs may stay away. There are a group of Labour MPs who may well vote for it.
"It could well get through. The challenge is going to be a concerted effort to talk it out by tabling large numbers of amendments.
"I think we've got a 50/50 chance in the Commons."
Mr Wharton argued that Tory position on Europe was "becoming more settled" adding that "over time there has been a noticeable trend, the party is becoming more eurosceptic, sceptical about the benefits of that relationship".
Councillor Jim Gifford, the leader of the Tory group on Aberdeenshire Council, told the conference the referendum should be held sooner.
"I would like a referendum much, much quicker so we can stop talking about it," he said.
"It's a distraction from all the other things we're doing.
"The day-to-day work on Europe needs to be sorted out PDQ and get this referendum out the way as quick as possible."
Meanwhile Scottish Tory MEP Struan Stevenson issued a warning to those Tories who wanted Britain to quit the EU.
He said: "Those people who think if we vote to pull out of the EU everything in the garden will then be rosy should look at Norway. Norway's main trading partner now is Europe. Norway pays as much in tariffs to be able to trade with Europe as we pay in our contribution to the European budget per capita. That is a fact.
"Norway has to sign up to all the rules and regulations that spew out of Brussels from the Brussels bureaucrats we all hate, and they have no seat at the table, no say in being able to alter or have any judgement on these rules and regulations.
"So everything isn't going to be resolved overnight by pulling out of Europe at all.Those people who are coming out with the more extreme views should look at the facts."