Ian Katz, deputy editor and head of news at the Guardian says:

I think that in many circumstances it is fine to accept trips funded by governments, NGOs or lobby groups, though in all cases we should declare them at end of the piece. All funded trips should be authorised by a senior editor and the judgment we should make is, ‘What would the reader, armed with the information about how the trip was funded, make of it?’ If the answer to that is that the reader would probably consider it dodgy, or somehow contaminating of our coverage, then we shouldn’t take it.”

http://www.guardian.co.uk/commentisfree/2012/apr/15/open-door-funded-trips