Alex Cole-Hamilton (right) celebrates becoming an MSP in 2016 at his office in Corstorphine with Scottish Liberal Democrat leader Willie Rennie, then Liberal Democrat Leader Tim Farron and former party leader Menzies Campbell. Picture: Greg Macvean

The Electoral Commission will focus on one key marginal seat in particular following a complaint from a member of the public.

The Lib Dems could face a stiff fine if found to have knowingly or recklessly flouted electoral law.

An investigation began earlier this month centred on the Edinburgh Western constituency and the Lothians region.

Sign up to our daily newsletter The i newsletter cut through the noise Sign up Thanks for signing up! Sorry, there seem to be some issues. Please try again later. Submitting...

Current MSP Alex Cole-Hamilton was a dual candidate at the 2016 vote - meaning he stood in both the seat and was also included on his party’s list vote.

According to electoral rules, dual candidates are expected to make an “honest assessment” of whether their spending promotes their constituency or list campaign. Parties are warned not to “split costs of an item if produced mainly to promote a candidate,” the Herald reported.

The Lib Dems regained the Edinburgh Western seat following an intense campaign which exploited an alleged financial scandal engulfing the then SNP MP for the area, Michelle Thomson.

The commission is understood to be examining why around £1950 identified by Mr Cole-Hamilton as list spending was apparently omitted from the party’s national return.

The MSP, now the party’s health spokesman at Holyrood, reported he spent £32,549 on his constituency campaign - £543 below the legal limit.

Lib Dem candidates in other Edinburgh constituencies spent an average of £924.

Mr Cole-Hamilton and his election agent were previously invesgitated and reported to the Crown Office but prosecutors dropped the case in October last year.