Continued severe winter weather in the UK resulted in only 81% of trains running on time in December 2010, compared with 80% for the same period last year, according to figures released by Network Rail.
The latest performance results from the period 12 December to 8 January 2011 included severe winter weather and the coldest December ever recorded in Great Britain.
Nine of the 19 operators saw their performance improve compared to the same period last year, while 12 operators saw significant movement in their performance over three percentage points.
London Overground was the most punctual operator during the period with 93.5% of trains on time, followed by c2c Rail with 89.4%, South West Trains with 88.2%, East Midlands Trains with 86.6%, and Chiltern with 85.5%.
The punctuality levels of Merseyrail, fell from 92.5% in December 2009 to 82.9% in December 2010.
First TransPennine Express recorded the biggest improvement in punctuality and ran 83.7% of trains on time in December 2010 compared with 75.7% in December 2009.
East Coast punctuality was 63.3% and Virgin Trains had 65.6% of trains on time, while First ScotRail reported a punctuality figure of 73.9%.