Some trains are carrying more than double their capacity as the network buckles under demand at peak times, new figures show.
Southern Railway's 7.16am East Grinstead to London Bridge train topped the list, with the service taking 1,366 passengers - 213 per cent of the 640 it was designed to carry.
The figures, from the Department for Transport (DfT), cover England and Wales and are based on standard class passengers travelling on weekday services in autumn last year.
The top 10 most crowded trains are:
- 1. 7.16am East Grinstead to London Bridge - Capacity: 640 - Passengers: 1,366
- 2. 7.55am Cambridge to London King's Cross - Capacity: 202 - Passengers: 426
- 3. 5.08pm Sutton to St Albans City - Capacity - 391 - Passengers: 758
- 4. 6.57am Brighton to Bedford - Capacity: 630 - Passengers: 1,215
- 5. 4pm Manchester Airport to Edinburgh - Capacity - 191 - Passengers: 357
- 6. 7.27am Reigate to London Bridge - Capacity: 669 - Passengers: 1,233
- 7. 5.18pm London Paddington to Oxford - Capacity: 242 - Passengers: 445
- 8. 4.22am Glasgow Central to Manchester Airport - Capacity: 191 - Passengers: 344
- 9. 4.26pm Bedford to Brighton - Capacity: 372 - Passengers: 669
- 10. 6.13pm London Euston to Birmingham New Street - Capacity: 412 - Passengers: 729
Overall, the average proportion of passengers carried on overcrowded trains in major cities was 3.8 per cent.
Campaigners have demanded improvements in the wake of the figures, arguing that commuters should not be expected to face year-on-year fare hikes if the situation did not change.
Lianna Etkind, from the Campaign for Better Transport, said overcrowding was making passengers' lives a "misery".
"People are rightly angry that they pay more in fares year after year, but never get a seat, and have to stand crammed into someone else's armpit," she said.
"With such high levels of overcrowding, the government cannot expect people to pay for yet another fares hike in January."
Anthony Smith, chief executive of passenger watchdog Transport Focus, added: "Continuing to invest in new trains, better frequency, track capacity and improved signalling will ultimately give passengers a better chance of getting a seat or at least stand in some comfort.
"In return for continuing fare rises passengers expect continued investment and improvement."