More trains on one of East Anglia's main lines to London were late this year in comparison with 12 months ago.
Train punctuality fell over the past year on East Anglian lines
Office of Rail Regulation figures for operator One's services show both intercity routes and local trains.
On the London line through Norfolk, Suffolk and Essex, only 78% of trains ran on time in the last quarter of last year but in 2004 84% were punctual.
One Railway blamed infra-structure failures for the fall in performance in this year's figures.
Peter Meades, a spokesman for One Railway, defended the train operator's record and said there are reasons for the poor performance.
"It was a challenging period all round and there were a number of factors which affected our performance but were outside our control," he said.
"These included a number of infra-structure failures on the main London line, several fatalities and over-running engineering works."
The rail regulator added that local services in the region, which also includes Cambs and Herts, also saw a drop in punctuality from 87% to 83%.
Nationally, 11 of the country's 24 train companies improved their running times year on year. The overall number of complaints also dropped slightly although there was a big increase in those about regional services.