IN A blow to the Coalition, key independent Tony Windsor has backed Labor's $43 billion national broadband network, criticising the opposition's cheaper alternative as a ''retrograde policy'' that would create a digital backwater in rural Australia.

Mr Windsor told The Sunday Age he believed Labor's national broadband network was the better of the two policies.

Mr Windsor, who was briefed by senior officials from the Department of Broadband last week, said he had been convinced that ''you do it once, you do it right, you do it with fibre''.

The comments come as Mr Windsor and the other two rural independents, Rob Oakeshott and Bob Katter, remain locked in negotiations with both sides to determine who they will ultimately support: Prime Minister Julia Gillard or Opposition Leader Tony Abbott.

Two weeks after the election, Mr Katter and Mr Oakeshott were yesterday bunkered in their Parliament House offices in Canberra. Last night the two men were seen walking outside Parliament House in blustery conditions deep in animated conversation. A senior Coalition source said it was disappointing they were not in their electorates to gauge the mood of constituents who are ''no doubt deeply concerned about the possibility of a Greens-Labor government''.