By-elections are key tests of electoral opinion, a snapshot of the mood of voters which very often captures the frustration with a governing party.
Rarely however are they a pointer to what will happen in a general election scenario.
However, any vote in Lanarkshire in the coming months could test that rule of electoral politics.
The expected poll at Rutherglen and Hamilton West following the suspension of MP Margaret Ferrier from the Commons for 30 days, allows voters in the constituency the opportunity to demand a by-election.
Ten per cent of registered electors can sign a recall petition which would see locals elect a new MP later in the year.
Ferrier’s troubles of course stem from her egregious breaches of Covid rules. From the moment she lost the SNP whip and knew that she would be prosecuted she became a lame duck MP.
Her constituents, as evidenced in vox pop after vox pop have by and large lost confidence in her.
Some in the Commons will say she has been treated unfairly and I have some sympathy with the view that her prosecution was not proportionate with her offence given others at Westminster were also engaged in rule breaking.
Nevertheless, at the point of alienation her position became untenable and she should have resigned if only to ensure that her constituents had a representative who could do a job of advocacy on their behalf free from the taint of scandal.
Why would anyone put themselves through more misery in full public glare?
The only explanation is that Margaret Ferrier decided to sit it out for another couple of years and bank a handsome salary in the process.
The optics are not good for those who argue that she is a decent woman who made some bad calls.
Taking money from the public purse when your constituents have lost confidence in you is not decent, it’s behaviour that is both stubborn and just plain wrong.
This will be the first Westminster by-election in Scotland since that held for Airdrie and Shotts in May 2021.
It was a low-key affair following the decision of Neil Gray to leave the House of Commons for Holyrood.
The by-election in Scotland prior to that was way back in 2011 following the death of David Cairns. Labour held Inverclyde at a time when their electoral fortunes were far greater than they have been in recent elections.
There are a number of factors that make this poll the most fascinating in a long time.
It would be a first in Scotland for a by-election to be held as a result of a recall petition.
It is one that will come probably within a year of a UK-wide general election and the implications of the poll could have profound consequences for all of the parties.
As a result, the media will crawl all over this contest in a way that Airdrie and Shotts, relatively speaking, went unreported.
For Labour, failure to win in this once heartland area would be nothing short of calamitous.
The circumstances of the previous MP’s behaviour is not exactly helpful for the SNP despite the fact Margaret Covid (as Nicola Sturgeon once called her) was kicked out of the SNP group at Westminster.
If Labour can’t win here, it suggests that any election victory for Sir Keir Starmer will have to be ‘made in England’ and that is not a great look for a party which says it wants to strengthen the union.
Victory will embolden Labour and simultaneously send a shiver through the SNPs Westminster contingent.
Many of them represent seats in west central Scotland which would suddenly appear vulnerable if Labour can build on the momentum of by election success.
What makes Labour’s task slightly easier is that fact that at the last election in this constituency, the Scottish Conservatives polled 8,000 votes.
Any material squeeze by Labour on this unionist vote would put then in a strong position to win.
Douglas Ross, the Scottish Conservative leader, got himself into a presentational and strategic pickle recently by suggesting Tories should vote Labour to oust the SNP in seats where Tories cannot win.
He then performed something of a volte face on the suggestion but only once the genie was well and truly out of the bottle.
His initial remarks and subsequent qualification in a sense were a storm in a teacup.
Unionist voters who do not want a Nationalist MP know what to do with the electoral arithmetic. With respect to Ross, they don’t need his encouragement to do the blindingly obvious.
The Tory campaign in Rutherglen is likely to be derailed by the issue of tactical voting. I cannot imagine too many UK ministers will be treading the streets of Rutherglen, Cambuslang and Blantyre in the months ahead.
A Labour win would be bad for the SNP and would therefore bring the Tories a measure of private comfort, but it would be yet another piece of electoral evidence suggesting their days governing the UK are about to come to an end.
One senior SNP MP told me recently that the party have factored in defeat in Rutherglen and that the issue is really the size of the Labour majority.
I was actually quite surprised that he was quite so sanguine. A defeat is a defeat. It will generate negative headlines. The size of the majority will merely dictate the tone of those headlines.
This is a bad time for the SNP to be trying to win in Rutherglen.
The party’s travails over internal finance are not helpful.
I bet the average voter could not offer a lucid commentary on all of the party issues, but they have a nose for something that smells bad.
And from the ferries fiasco to the deposit return scheme and more significantly the creaking NHS, there is a sense in which Humza Yousaf is under the cosh on a near daily basis.
Defeat would be bad. A heavy defeat will lead to a barrage of negative headlines and a narrative about his inability to stamp any authority on his leadership and on the office that he holds.
Victory for the SNP would confound the pundits and give him the confidence booster he so badly needs.
Rutherglen and Hamilton West will therefore be no ordinary by-election.
It is likely to have an echo in the politics that will help shape the outcome of the next UK general election.