Footfall on the UK high street fell 2.2% in October and UK traffic to online retailers decreased by 0.5%, according to Experian.
Experian said that too much new retail space - 3 million sq ft of new space has come on stream this year - had contributed to falling numbers.
Jonathan de Mello, director of Experian's retail consultancy said: "This year has seen the opening of an unprecedented number of new shopping centres and whilst some have clearly moved their towns up the retail rankings, such as Liverpool from 15th place to 5th place, others have had less of a positive impact, particularly in the current economic climate."
"For every winner there is a loser and Liverpool has clearly had a negative effect on nearby towns such as Wigan, and even on the rest of Liverpool itself, with John Lewis moving into the new Liverpool One scheme."
De Mello added: "Retailers may be hoping that the pre-Christmas reduction in the cost of petrol may translate into extra cash to spend on the high street. But as we get closer to Christmas, there will inevitably be winners and losers, and this year it is the discounters, value chains and supermarkets that are expected to come out on top."
Separately, Robin Goad, director of research at Hitwise, which measures internet traffic and which is owned by Experian, said: "UK internet traffic to online retailers decreased by 0.5% between October 2007 and 2008, the first annual decline this year. Up until now, online retail has been surviving the economic downturn, but this month's data proves that the sector is not immune."
Retailers also suffered a significant rise in business failures according to the latest Insolvency Report and Distress Index by Experian. Business failures in the non-food retail sector rose by 17.4% compared with last October. At the same time, retailers seeking administration orders leapt by 52.9% in the last 12 months and 31% in the last month alone.