There were 320,000 telephone numbers registered on the Corporate TPS by May 6 and 51% of locations registered had only one to five employees at the business site.
However, Experian said that the proportion of large companies registered compared with the overall UK business population is higher than the proportion of small companies registered.
Experian also looked at the type of companies registered and found that manufacturing firms were most likely to register with the service.
Richard Lloyd, director of Experian's B2B Marketing division, said: "One year on from its inception, it appears to be the local car parts factory rather than the small corner shop that has been attracted by the Corporate TPS."
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