A morning train from West Sussex to London is the most overcrowded in England and Wales, new figures show.
Southern's 07:16 BST service from East Grinstead to London Bridge usually has more than double the passengers it was designed to carry.
The Department for Transport (DfT) data showed 1,366 people typically crammed into 12 carriages designed for 640.
The DfT said improvement works were under way as some customers had "not received the service they deserve".
Lianna Etkind, of the Campaign for Better Transport, said: "Overcrowding continues to make passengers' lives a misery.
"People are rightly angry they pay more in fares year after year, but never get a seat, and have to stand crammed into someone else's armpit.
"With such high levels of overcrowding, the government cannot expect people to pay for yet another fares hike in January."
Jacqueline Starr, managing director of customer experience at the Rail Delivery Group, which represents train operators and Network Rail, said they "understand passengers' frustration when they can't get a seat", but additional carriages cannot be added to the train.
The DfT said when the Thameslink Programme is completed next year there will be extra services on routes south of London to boost capacity.
A spokesman added: "Rail passenger journeys have more than doubled in the last 20 years. We are committed to improving journeys and we are delivering more trains, more seats and quicker journeys to meet this record demand.
"We are investing £40bn in our railways and by the end of 2019 we will have more than 3,700 new carriages on the network.
"We know some passengers have not received the service they deserve, and we continue to work with the industry to cut journey times and crowding, improve reliability and deliver more frequent services."
The most overcrowded trains
- 07:16 BST East Grinstead to London Bridge
- 07:55 BST Cambridge to London King's Cross
- 17:08 BST Sutton to St Albans City
- 06:57 BST Brighton to Bedford
- 16:00 BST Manchester Airport to Edinburgh
- 07:27 BST Reigate to London Bridge
- 17:18 BST London Paddington to Oxford
- 04:22 BST Glasgow Central to Manchester Airport
- 16:26 BST Bedford to Brighton
- 18:13 BST London Euston to Birmingham New Street
The figures relate to standard class passengers on weekday services in autumn last year.