The reception is hardly one Nicola Sturgeon can have been hoping her tartan army would receive on their arrival at Westminster.

Two weeks on from the Election, the longest-serving member of the House of Commons, Gerald Kaufman, issued a withering assessment of the behaviour of the unprecedented intake of 56 Scottish Nationalist MPs (up from just six in 2010).

‘I think that their conduct is infantile,’ said Mr Kaufman yesterday. ‘They’re goons, and if they go on like this, instead of using their undoubted mandate from the Scottish people to be serious about issues on behalf of Scotland, they will devalue themselves.’

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Mhairi Black, a 20-year-old student who became the country's youngest MP since the 17th century, posed eating a 'quintessentially Scottish' lunch, consisting of a plate of chips, bread and a packet of cola cubes

Meanwhile Roger Mullin MP was pictured leaning on the despatch box used by the Prime Minister by his SNP colleague Brendan O'Hara MP, with the caption: ‘Never let it be said Roger Mullin lacks ambition.’

Mr Kaufman is not alone at Westminster in his view of the new SNP members’ boorish and puerile antics: day after day since election night, they have displayed an uncanny ability to make headlines for the wrong reasons.

Indeed, they have conspired to fill far more column inches by breaking Parliamentary rules, indulging in PR stunts and starting petty fights with rivals, than by advancing their supposed political agenda.

The party’s first week in Westminster was dominated not by talk of the SNP opposing Tory ‘austerity’, but by tales of members carousing in Commons bars and scoffing subsidised junk food in its restaurants. Its new intake of MPs generated further hostile news by taking ‘selfies’ in the Palace of Westminster (in deliberate breach of rules that outlaw photography there), rudely ignoring requests not to clap in the Commons chamber, and brashly evicting the Lib Dems from offices they’d occupied for more than a century.

Their second week in Westminster, which began on Monday with the election of the Commons Speaker, saw Scotland’s new lawmakers mount a bizarre effort to force 83-year-old Labour MP Dennis Skinner to give up his customary front-bench seat in Parliament. (It was the attempt to oust Skinner that led to Kaufman’s stinging rebuke.)

In a further twist, the official swearing-in of new MPs descended into farce when one left-wing SNP member, Hannah Bardell, was required to take her oath twice after she ‘forgot’ to mention the Queen the first time.

Later, a colleague, Natalie McGarry, a fierce anti-monarchist, used Twitter to disown the vow she had just taken.

‘As long as in your heart and your head you believe sovereignty lies with the people, doesn’t matter what comes out your mouth,’ she declared.

These antics are hardly in keeping with the SNP’s tone during the recent election campaign, when its leader Nicola Sturgeon promised to pursue ‘grown-up politics’.

Indeed, Ms Sturgeon is understood to be deeply concerned that her new MPs are displaying what one ally calls a ‘chippy, confrontational, and at times very puerile’ attitude since arriving in Westminster.

On Thursday, someone described as a ‘senior SNP MP’ broke ranks — albeit anonymously — to warn his colleagues that their recent behaviour is giving the party a bad name.

‘Behave yourself and act like adults,’ he told fellow MPs. ‘Don’t go causing unnecessary fights. We are here to represent our constituents. It is serious business.’

The remarks, said to have been issued with the approval of Ms Sturgeon, may on the face of things seem perfectly straightforward.

Yet behind the scenes, they are anything but. For informed observers believe they represent not just an attempt to curb the excesses of some of the party’s fresh intake of MPs, but also a coded criticism of the way Sturgeon’s predecessor as SNP leader, Alex Salmond, is influencing their behaviour in London.

Manchester MP Gerald Kaufman described the new SNP intake as 'goons' and their behaviour as 'infantile'

Now he is an MP, Mr Salmond is, after all, by some way the party’s most prominent figure in Westminster, and this week he insisted ‘the days of Scotland being stuck in the back corner and ignored are over’.

Salmond is understood to approve of a proposal recently floated by ‘senior’ SNP sources in Westminster for Scotland to hold a second independence referendum without the Prime Minister’s permission, should he refuse to sanction one.

Ms Sturgeon is, crucially, vigorously opposed to such a plan. Little wonder, therefore, that recent events have sparked rumours of a growing power struggle between the two politicians.

‘There is a faction of the SNP, in which Salmond is prominent, who believe it’s good politics to annoy the English and upset the Westminster establishment with these quite petty japes and stunts,’ says one veteran observer of the party.

‘They think Scottish voters will see it as getting one over on the auld enemy. They think it should continue indefinitely.

‘Ms Sturgeon strongly disagrees and wants MPs to concentrate on pursuing the party’s political agenda and helping their constituents. But she’s stuck in Edinburgh, 300 miles away, which makes maintaining discipline in London very tricky.’

So it seems. For the SNP’s efforts to cock a snook at Parliamentary authorities appear to have begun in earnest just a few hours after its MPs arrived in Westminster. First to make waves on this front was Roger Mullin, the new MP for Kirkcaldy and Cowdenbeath. On an induction tour of the Commons chamber, he decided to pose for a jokey photograph while leaning on the despatch box used by the Prime Minister.

The image was then uploaded to Twitter by colleague Brendan O’Hara, with the message: ‘Never let it be said Roger Mullin lacks ambition.’

Meanwhile, two fellow MPs, Neil Gray and Douglas Chapman, took ‘selfies’ on the Commons’ green benches, while Mhairi Black, a 20-year-old student who became the youngest MP since the 17th century, posed for a tweeted photo on the Commons terrace.

Black was eating a quintessentially Scottish lunch: chips, bread, and a packet of cola cubes. ‘You can take the girl from Glasgow …” read the image’s caption.

Ms Sturgeon is reportedly at odds with former SNP leader Alex Salmond, who wants to hold a second referendum on Scottish independence, even if Prime Minister David Cameron doesn't sanction one

To an outsider, these pictures may have seemed harmless enough. But taking photographs in the Palace of Westminster represents a serious breach of protocol, and journalists, or members of the public, caught doing it risk immediate arrest. The Sergeant-at-Arms, in charge of enforcing Parliamentary rules, let it be known that the photography should cease. However, the party’s MPs continued to post them online for several days.

As recently as Thursday, Calum Kerr used Twitter to share an image of himself on the terrace. Just days earlier, Angus MacNeil posted one of a committee room.

It wasn’t until yesterday that the party’s chief whip, Mike Weir, succeeded — reportedly at Ms Sturgeon’s behest — in making his MPs call a halt to the selfies.

Elsewhere, the social habits of the new MPs, who have been largely billeted at the £200-a-night Park Plaza, a short stagger over Westminster Bridge, are generating their fair share of unhelpful coverage.

Take the aforementioned Mr MacNeil. On election night, he claims to have attempted to down a drink for every SNP gain, and last week told a reporter: ‘I got as far as 43.’

Tommy Sheppard, a comedy club impresario who won in Edinburgh East, has reported draining an entire bottle of Oban whisky with his agent on election night, before moving on to a second bottle — ‘A special one I got for my birthday’.

‘It wasn’t really a celebration, more an anaesthetic,’ he claims.

What does the sober Ms Sturgeon think of such comments? She has yet to say, but they seem at odds with the ethos of a party which has — in an effort to clamp down on binge drinking — endorsed minimum pricing on alcohol.

In Westminster, the SNP MPs’ celebrations have nonetheless continued in earnest.

‘The new Scottish battalion chooses as its Commons howff [headquarters] the Sports and Social Club, located in a basement near the rubbish bins,’ wrote George Kerevan, new MP for East Lothian, in a diary for the Scotsman newspaper, last week. ‘Inside, this looks and feels like a Glasgow pub.’

According to one Westminster blog, Mhairi Black (who once dubbed the vodka-based Smirnoff Ice ‘drink of the Gods’ on her Twitter feed) was spotted there drinking ‘snakebite’ — an intoxicating drink popular with teens, which consists of half a pint of lager, half a pint of cider and a shot of blackcurrant cordial.

So visible and constant is the contingent of SNP members in the subsidised bar that it was reported last week that members are now nicknaming it the ‘Rabbie Burns’.

At least the atmosphere there remains convivial. Which is more than can be said for relations between the new MPs and their colleagues from other parties.

The Lib Dems, for example, are reported to be deeply put out by the manner in which the SNP recently evicted their whips from their offices on a prime Commons corridor, which they have occupied for over a century.

The SNP's 56 MPs at the Houses of Parliament, following their first meeting. There has been reports that some of the group have been drinking heavily as their post-election celebrations continue in earnest

‘Since the SNP is now the third largest party, they are perfectly entitled to the offices and the Lib Dems were of course happy to give them up,’ I’m told.

‘But the manner in which they took over was quite unpleasant. Essentially, someone with a Scottish accent marched in, ordered the occupants to leave, and started gloating about how they were going to chuck out all the historic photos of Gladstone [the great 19th-century Liberal statesman] and rename the corridor Freedom Alley.’

The Tories meanwhile are irked by an incident in which the veteran MP Simon Burns was heckled while giving a speech to a group of new SNP members about protocol.

Mr Burns, who had generously volunteered to make the presentation in the Commons chamber, politely informed the new MPs that clapping is not allowed during debates. Their response? A noisy round of applause — which they then boasted about on Twitter.

‘People have clapped in the chamber, which for MPs like me is totally unacceptable,’ Mr Burns complained afterwards. ‘You don’t clap in the chamber, you say “Hear, hear” or if you’re in a sedentary position you shout “Rubbish”. It is just not the way you behave in the chamber.’

Others have been angered by a speech that Angus Robertson, the SNP’s leader in Westminster, gave in the House following John Bercow’s re-election as Speaker. According to Parliamentary tradition, his remarks were supposed to be apolitical — but he chose to goad rival parties in Scotland by repeatedly describing them as now being ‘really small’.

That was nothing, however, compared to the SNP’s petty attempt to deprive Dennis Skinner of his usual seat in the Commons — an incident in which Alex Salmond was reportedly involved.

Alex Salmond MP (left) was reportedly involved in a plot to take veteran Labour MP Dennis Skinner's usual seat in the House of Commons off him, a spot he has sat in since the 1980s and is traditionally allowed to keep

The veteran Labour MP, fondly known as the Beast of Bolsover, has occupied a specific spot on the front-row bench on Labour’s side of the House since the Eighties — a seat he is traditionally allowed to keep.

The SNP’s leaders are expected to sit alongside him on the same bench, and on the bench immediately behind it. But that was not good enough for the SNP. They wanted Mr Skinner’s seat as well.

The problem is that no formal Parliamentary rules actually govern who sits there, and the chair is in theory available to whoever gets there first to reserve it.

With this in mind, on Monday Peter Wishart, the SNP member for Perth and North Perthshire, recruited colleagues to spend several hours (in the middle of what was supposed to be a work day) occupying the benches in question — and Skinner’s favoured seat — on a rota system.

The plan fell apart late in the morning when police officers asked the SNP’s members to move, so they could conduct a ‘security sweep’ of the chamber. A passing Labour MP, Kevan Jones, sneaked in, reoccupied Skinner’s seat and refused to leave.

There followed what one witness described as a heated dispute, in which Wishart returned and ‘came screaming over, saying, “This is outrageous”.’ However, Jones held his ground and eventually Skinner got his seat back.

‘They are supposed to be the Left-wing, anti-austerity party, so why do they think it’s a good idea to try to throw out Dennis Skinner?” Mr Jones asked, when we spoke this week. ‘He’s not part of the Establishment. It can’t be good, making life misery for a bloke who is 83.’

The dispute over the seat has still to be formally resolved and the House of Commons may yet play host to a surreal game of musical chairs over the coming weeks.

‘Individually, the new SNP members are perfectly nice,’ Mr Jones added. ‘The problem is that one or two of their leaders want to portray themselves as victims of the Establishment. So they are carrying on this charade.’

The SNP, for its part, isn’t giving an inch. ‘We are the third party and we will make sure the House sees that,’ is how Peter Wishart put it.