If any of those decided to downgrade UK governmental bonds, then the cost of borrowing the current debt would rise and it would be even harder to pay off.
During the election campaign a lot of noise was made about £8billion of cuts in public spending that the conservative party wanted to make, if UK debt is downgraded, the extra interest payments would end up costing another £10billion http://www.guardian.co.uk/business/2010/may/07/how-safe-uk-aaa-credit-rating - more than wiping out any benefit to doing this and causing the public sector deficit to increase still further.
I don't like this situation; I think the ratings agencies have far too much power with no effective oversight, and I think it is a major failure in the UK political system that the government was able to generate so much debt in the first place, but simply calling the current situation 'neo-liberal propaganda' won't change this reality and certainly won't make it go away.
Nonetheless, I don't think there is likely to be as much support for 'public-private partnerships' as you assume.
Over the last decade or so, Labour have used a lot of them, and they proved convenient insofar as they allow an multiple announcements of public spending projects to be made while hiding the cost from balance sheets for several years - but with existing lines of credit already running thin, the market is likely to take a dim view of any such 'hidden' commitments to public spending.
In the only place where there is direct executive power currently held by a the conservative party - The London Mayoralty - Public Private Partnerships have been wound down, indeed Boris Johnson only this week ended the PPP deal with tubelines for rebuilding the London Underground.
I don't claim that such a move is beyond criticism, in particular the compensation payment that tubelines has received from this looks to be excessive. Not only that, but when the books so urgently need balancing, then a long term infrastructure project such as rebuilding the tube may be the sort of thing that is canceled completely.
The difficult we do today; the impossible takes a little longer.