Complaints about Southern rail's parent company Govia Thameslink Railway (GTR) rocketed over 300 per cent in the third quarter of last year and accounted for nearly a fifth of all complaints made nationally.
The 347.1 per cent rise came from the Office of Rail and Road (ORR)'s latest stats on complaints made by passengers regarding rail services in Great Britain.
Nearly a third of GTR complaints were about punctuality or reliability and 23.9 per cent were about the delay compensation schemes.
Its complaint rate was 32.1 per 100,000 journeys, while the national rate was 29.4 complaints per 100,000 journeys for the third quarter of 2016-2017, broadly in line with the year before at 29.5 complaints per 100,000 journeys.
A GTR spokesperson said:
These figures are disappointing but not surprising.
This time last year, our complaint rate was one of the lowest in the industry. Since then, the onset of industrial action led to a sharp rise in the number of complaints.
Now, as the performance of our train service improves, complaint rates are falling once again.
The latest quarterly data refers to October, November and December last year; when Southern rail was in the midst of severe industrial action by train drivers' union Aslef and the Rail, Maritime and Transport (RMT) union. It has since reached a deal with Aslef though that's still to be put to members, and offered the RMT fresh talks earlier this week.
It wasn't just GTR that recorded a significant increase though; complaints on South West Trains surged 71.5 per cent and on Southeastern by 33.3 per cent, while Greater Anglia complaints increased by 18.3 per cent.
The four London and South East train companies accounted for over half of all national complaints.
Liberal Democrat transport spokesperson Jenny Randerson said:
The service delivered by some operators is something that would damn a developing country.
In any other job, in any other industry, the bosses who have presided over months and months of misery would be held to account yet these bosses aren’t.
The government should take responsibility and should have stepped in many months ago to stop this chaos.
Of the total complaints across the board, 28.5 per cent were about punctuality or reliability, 8.1 per cent about ticket buying facilities and 6.5 per cent about there not being sufficient room for all passengers to fit.