The SNP’s historic landslide at the general election guarantees Mr Robertson a slot at every Prime Minister’s Questions and will hand the party the chairmanship of some Commons committees.
It left Ukip MP Douglas Carswell (Clacton) standing at the bar of the House while the handful of Liberal Democrats - not all of whom attended - were stuck three and four rows back.
But the delegation was not strong enough to dislodge Dennis Skinner, the veteran Labour MP for Bolsover, who for now at least held on to his seat on the front corner of the far opposition bench, across the aisle from Labour chief whip Rosie Cooper and close enough to the Prime Minster to have his shouts heard. Left-winger Ian Lavery also held his ground by sitting on the front bench.
Mhairi Black, the baby of the House and SNP MP for Paisley and East Renfrewshire, found herself in the mass of Labour MPs sitting next to Diane Abbott (Hackney North and Stoke Newington) and behind the main opposition front bench.
It was not clear whether Ms Black chose the seat deliberately or was simply in the wrong place on her first day as an MP.
Moray MP Mr Robertson thanked Mr Bercow for treating the smaller parties fairly in the last Parliament when his party had just six MPs compared to the 56 today.
He said: “The SNP has returned with a great many more members than were here in the last Parliament.
“We represent 56 of Scotland’s 59 constituencies, we are now the third party in this House and we look forward to making Scotland’s voice heard.
“We look forward to opposing austerity and we will resolutely oppose the renewal of Trident weapons of mass destruction.
“We will have our voice heard and we will play a full and fair part in the proceedings of this House of Commons.
“We still, however, support the fair treatment of small parties - small parties like the Liberal Democrats and the Green Party and the other really small parties, who only have one member, like the Scottish Conservative Party, the Scottish Labour Party and and the Scottish Liberal Democrats.”