A total of 91.3% of trains ran on time in the period July 21 to August 17, Network Rail (NR) said.
This compared with a figure of 92% in the same period last year.
The poorest late-summer punctuality was on the two main London to Scotland routes - East Coast and the Virgin-run West Coast.
Only 85.7% of East Coast and only 86.2% of West Coast trains were on time. Delays attributable to NR accounted for 69% of the East Coast delays.
The Office of Rail Regulation (ORR) has warned NR about its punctuality record, particularly on the long-distance routes. Virgin Trains has also been particularly unhappy with NR's punctuality on West Coast.
Virgin's request to run extra services on the West Coast line was turned down and it has re-applied to start the services from next May.
But to its annoyance, Virgin has learnt that NR considers it is unlikely that it will be able to offer these services until autumn 2014 at the earliest.
In the period July 21 to August 17, the best-performing train company was the London to Tilbury and Southend operator c2c which ran 97.5% of trains on time.
"In order to provide the standards of service and punctuality expected by passengers and its customers, NR must quickly improve the management of its assets and catch up on planned renewal work to improve resilience, reliability and punctuality on Britain's railways."
A spokesman for the Association of Train Operating Companies said: "More than nine out of 10 trains arrived as planned according to the government set measure for punctuality.
"Train companies will continue to work with NR and focus efforts on providing passengers with an even better service."
Manuel Cortes, leader of the TSSA rail union, said: "The only thing that runs on time on our railways is fare rises. They happen every 12 months despite how poor the service is that passengers have to suffer.
"Despite these latest figures, (average season ticket) fares will go up in January 2014 by 4.1% just 12 months after going up by 4.2% in January 2013. Whatever happens, it is always the poor passengers who have to pay through the nose."