The SNP is facing a probe by parliamentary watchdogs over allegations it broke rules by auctioning Holyrood lunches with the First Minister and his deputy to raise party funds.

It was revealed on Thursday morning that guests at an SNP fundraiser in Glasgow had paid £11,000 to lunch with Alex Salmond and Nicola Sturgeon at the Scottish Parliament restaurant.

And on Thursday afternoon, a Parliament Spokesperson confirmed that Mr Salmond and Ms Sturgeon had written to Holyrood authorities to seek clarification. A spokesperson said that a report would now be prepared.

Its statement said:  "The policy on the use of parliamentary resources states that parliamentary resources are provided by the SPCB to support Members with their parliamentary duties.

"These resources, which include the Members restaurant, must not be used for any other purpose, including any significant party political purposes.

"We understand that the relevant Members are concerned over this matter, and will be writing to the parliamentary authorities to explain their position. 

"Once officials have established the facts, the SPCB will receive and consider a report."

MSPs are banned from using the "parliament campus" for party fundraising activities. The SNP insisted the lunches were within the rules because the auction was held at a Glasgow restaurant.

Lunch with Ms Sturgeon raised £2000 while someone paid £9000 to dine with Mr Salmond. The cash is set to go towards the campaign of Osama Saeed, the party's candidate in the Glasgow Central seat at Westminster.

The party says it has broken no rules because the fundraiser was held outwith the Holyrood "campus" in a Glasgow restaurant.

However, opposition politicians have accused the party of "cash for access" arguing that MSPs would normally only host dinners at the parliament when they are raising money for charity.

Just hours after information about the scandal was revealed, the Labour Party demanded an independent inquiry by sleaze watchdogs.

Former Secretary of State for Scotland Des Browne said: "These allegations are particularly serious. Salmond's parliamentary duties do not extend to using the Scottish Parliament restaurant to raise money for electing candidates.

"This is industrial-scale fundraising using parliamentary facilities and an abuse of public money. Cash for access demeans the office of First Minister.

"He must make a public statement about why he allowed himself to be placed in such an unwise position."

On Thursday afternoon, Scottish Labour Leader Iain Gray wrote to the First Minister demanding he explain his conduct, saying: "During the recent expenses scandal we have prided ourselves at Holyrood on our standards of behaviour and the transparency of our system.

"Alex Salmond has to explain how his £9000 lunch is connected in anyway to his duties as First Minister or an MSP."

MSPs must abide by rules which state that the "parliamentary campus should only be used for events relating to a Member’s parliamentary duties.”

In 2007, Tory leader David Cameron was rebuked by the Westminster authorities for hosting lunches and granting access to his House of Commons office to party members who paid a £50,000 subscription to the party's leaders group.

He later issued an apology for the cash raising exercise and on Thursday, the Liberal Democrats said the scandal should have been a lesson to other politicians.

The party's Chief Whip at Holyrood, Mr Rumbles, said: "Scottish Ministers should not be available to the highest bidder.

"I'd have thought that Alex Salmond and Nicola Sturgeon would have learned from David Cameron's cash for access scandal."

"We've worked hard in the Scottish Parliament to be as open and transparent as possible and we look to our most senior ministers to set an example."

The SNP auction was held at a fundraising dinner for Mr Saeed at the Kabana restaurant in Ms Sturgeon's Govan constituency. Guests paid £15 each for a ticket with the lunches making the most money from bidders.

An SNP spokesperson said: "Lunch with parliamentarians has been a fundraising opportunity across the parties for many years, and is not contrary to any current parliamentary rules.

"An obvious requirement is that the MSPs concerned pay for the lunch, which takes place in a public space. And all donations to the SNP are publicly declared in the normal way."

The event was organised by the Scots Asians for Independence group and was attended by around 200 people from Glasgow's Asian community.

Mr Saeed, chief executive of the Scottish-Islamic Foundation, is standing in a key seat for the SNP. Glasgow Central overlaps with Nicola Sturgeon's Holyrood constituency and the party is hoping to build upon her Scottish election success.