The source of all the data will be Companies House. You can get (presumably unlimited) access to all annual returns for £17.5k pa [1]

I can't imagine the government make enormous sums of money through the sale of such data, and I think there is a significant public interest in this kind of company data being freely available.

[1] http://www.companieshouse.gov.uk/toolsToHelp/ourPrices.shtml