The deal, which is expected to be signed in the next couple of weeks, will see Royal Mail sort post for TPG to deliver.
The terms of the deal are expected to be the same as those agreed with Deutsche Post and UK Mail, where TPG will pay 13p for every letter sorted by Royal Mail.
In January UK Mail, a subsidiary of Business Post, became the first private company to gain access to Royal Mail's delivery network, breaking its 300-year postal monopoly and heralding competition in the UK postal market.
On Friday Postcomm chairman Nigel Stapleton said that he expected the UK Mail deal to lead to many others and said that the document should ensure that agreements could be reached more quickly in the future.
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