Southern has recorded some of its worst punctuality figures in at least six years.
Just 67.9% of its metro services - which operate in London and surrounding areas - arrived at their destination within five minutes of the scheduled time in the four weeks to December 10, according to Network Rail data.
Press Association analysis found this was the poorest performance for that route in any four-week period in publicly available records, which date back to April 2010.
Mainline and coastal services run by Southern - whose parent company is Govia Thameslink Railway - had an even lower figure of 56.7%.
Passengers using two other rail services run by GTR also suffered from the worst punctuality figures for those routes in Network Rail's records.
Thameslink scored just 60.1% while Great Northern was at 65.1%.
Another GTR service, the Gatwick Express, recorded a punctuality figure of just 62.3%.
A GTR spokesman apologised for the performance of its services, adding that there were a number of contributory factors.
He said: "This reflects the significant impact that the wholly unjustified industrial action being taken by Aslef and the RMT is having and the on-going additional knock-on delays from the London Bridge redevelopment.
"There have also been performance issues on Great Northern caused by weather, signal failures in key locations and problems with the ageing trains we have begun to replace on this route.
"We're sorry - our passengers deserve better and, together with Network Rail, we're working hard to improve performance."