The SNP is on the verge of "making history" by winning more Scottish seats at Westminster than any of the other parties, its campaign director said.

Angus Robertson predicted that when voters across the UK go to the polls in May the "SNP can become the largest party in the Westminster elections in Scotland".

He spoke out at the start of the SNP's campaign conference in Glasgow, which has attracted a record 3,000 activists, according the party bosses.

While the nationalists failed to win independence in last year's referendum, the party has seen a massive surge in support, and now has 100,000 members, making it the third biggest political party in the UK.

Its best result in a general election was more than three decades ago, when 11 SNP MPs were elected in October 1974.

Mr Robertson, the SNP Westminster leader, said: "We can make history in this Westminster election. I believe with hard work and with the positive SNP vision - we can win this election."

He told party activists: "We take nothing for granted - but we know what is possible. Let's make it happen."

Polls are predicting Nicola Sturgeon's party could wins dozens of seats north of the border on May 7, and may hold the balance of power in a hung parliament

Mr Robertson said: "The best ever SNP Westminster result was 30% of the vote when the SNP won 11 seats in 1974. I believe this year we can do better. I believe we will do better."

But he stressed that the result was "not certain".

He added: "The polls suggest it may well happen. Those of us that are knocking on doors, we know that it can happen, but we will not take anything for granted. And we will work every hour of every day until the polls close in that general election to secure an SNP victory across the length and breadth of Scotland."

Mr Robertson continued: "Of course the Scottish Labour leader Jim Murphy says his party will not lose a single seat and the Liberal Democrats say they will resist gravity and hope the people of Scotland will forget them cozying up to the Tories. I've got news for them as well, they are going to lose seats just like the Labour Party right across Scotland.

"We are going into this election in the strongest pre-election phase of support in the party's history, with our 100,000 members making us the third largest political party in the UK and this is the biggest SNP conference yet with 3,000 delegates here."

He said that more seats for the SNP would bring about "more influence and power for the people of Scotland"

He pledged: "We will play a constructive role in Westminster and bring our ideas forward in a positive spirit. We will offer a real alternative to the drab Tory-Labour cuts consensus. It is time for a more responsible economic policy. One which boosts long term growth, creates jobs and delivers all.

"We will invest in childcare and vital public services, we will not waste a £100 billion on a new generation of Trident nuclear weapons. We will make sure Scotland's NHS is always cared for, its budget protected and its future secure in public hands. And we will keep Westminster parties to their promise of more powers for Scotland.

"It is good ideas and hard work that win elections - not opinion polls. So hard graft, humility and a daily determination to earn the trust of the people of Scotland, these will be the hallmarks of the SNP campaign. We take nothing for granted and will work harder over these next 40 days than we have ever done before."

Meanwhile SNP MEP Alyn Smith told delegates the party's London branch now has more members that the entire Scottish Liberal Democrats.

"Let's look forward to after the Westminster election when there's even fewer of them," he added.

Opening the conference Europe and International Development Minister Humza Yousaf said that a large team of MPs at Westminster could "lock out the Tories from Number 10 and ensure Scotland's voice is heard".

He added: "That will happen if we pound every pavement, climb every tenement, persuade every person and chap every door."

The Scottish Government minister also warned Westminster politicians that nationalists would make them pay for impact of their austerity economics.

He said: "In this city alone we have the tragedy of tens of thousands of people queuing up for foodbanks, due to Tory and LibDem cuts

"Here in the 21st century, people are having to ask for a handout for bread and milk. For those Westminster politicians that have forced them into poverty let me say loud and clear: Shame on you, Scotland will make you pay."

Mr Yousaf said: "Six months ago we dared to dream. After the referendum our opponents thought they had put Scotland back in the box.

"Let it ring out from this conference, right here and right now, we are no-one's branch office, nobody put Scotland in a box.

"And as we dream, we believe more than ever before that independence will deliver a better future not just for us but for generations.

"Anybody who thinks that dream is dead, it is not. Believe me, independence is coming and it is coming for all that."

Mr Smyth later issued a clarification on Twitter saying: "There's more members SNP London branch than were at LibDem conference, not total members. Got that wrong, sorry."