Parliament’s standards watchdog will not investigate the expenses of MPs involved in the so-called ‘SNP love triangle’.

Kathryn Hudson, Westminster’s Standards Commissioner, has decided not to the probe the claims of Stewart Hosie and Angus MacNeil.  

But another watchdog, the Independent Parliamentary Standards Authority (IPSA), set up in the wake of the 2009 expenses scandal, said it was still "assessing" the case. 

Read more: After the affair ... Sturgeon set for showdown with Hosie in Westminster​

Mr MacNeil, who split from his wife last year, is alleged to have had a relationship with freelance journalist Serena Cowdy, 36.

She also had an affair with his colleague Mr Hosie, who announced earlier this month he was separating from his wife, Scottish Health Secretary Shona Robison.

Read more: Sturgeon vows 'love triangle' claims will not affect SNP​

Reports suggest that Mr MacNeil conducted his affair at the Park Plaza hotel in London's Waterloo, where he was staying at the taxpayers' expense.

The SNP insists that any suggestions of financial impropriety are "totally wrong".

Party sources said that overnight guests in MPs' hotel rooms incur no extra cost to the taxpayer and MPs are not required to register guests with Ipsa.

A spokesman for Ms Hudson said: "The commissioner has received a complaint but she has decided not to begin an inquiry."

Read more: Stewart Hosie resigns as SNP's deputy leader citing stress from media scrutiny into private life​

She is required to consider whether or not a complaint falls within her remit and if there is sufficient evidence to justify a full-blown inquiry.

A spokesman for the Scottish Conservatives, who reported the case, said: "We respect the decision of the Standards Commissioner. Our view is it is right to question such cases to ensure that public funds are always used in support of parliamentary duties."

An IPSA spokesman said: “We are still assessing the situation and no decision has been made”.