A minister's salary, like the whole apparatus of government, of whatever party, is paid from the public purse: minister and government are answerable to the public on matters of public interest. This should have nothing to do with party officials.
Mr Barton, and all members of news media seeking official access to ministers on matters of policy, should bypass Mr Hill and go straight to the civil servant responsible. If this turns out to be one and the same person, as seems to be Peter Mandelson's aim, that person should be under obligation to act as civil, rather than party, servant.
It is grotesque that a party official should take it upon himself to decide when government members should or should not appear to answer questions on policy. The party news management view is obviously that a press release be printed and read an air, commentators say "Oh, how wonderful," and leave things at that.