Manukau Mayor Sir Barry Curtis is furious at what he sees as a bid by the Auckland Regional Council to scuttle plans for a long-awaited rail link to the heart of his city.

The regional council is not only seeking a review of the 1.8km link's priority ranking against other rail projects but is also suggesting a free bus service be tried along the route, from central Manukau to the southern line at Wiri.

Council chairman Mike Lee denied yesterday that this was a bid to undermine Sir Barry's case for the $40 million to $50 million link, calling it a useful test of demand for public transport along the way.

"As far as I know there has been no business plan for a spur rail line - this will be a good litmus test of support," he said.

"It will help to create patronage."

He noted that Sir Barry and the Manukau City Council had asked the Auckland Regional Transport Authority to consider conducting a free bus trial within his territory.

Despite rising costs of subsidising fare-paying bus services, Mr Lee said, the regional council had finally resolved to ask the transport authority to give priority consideration to a free trial along the proposed rail route.

"Sir Barry has asked for a free bus trial and we couldn't think of a better place to put it," he said.

But the council's transport policy committee also last week resolved to ask the authority to examine justification for the Manukau link, which the Government has listed among four "core" rail projects to be completed within three years.

Committee chairman Joel Cayford, who proposed that resolution, went further yesterday in telling the Herald that a 1.8km link made more sense if it were part of a wider network and he believed a busway out to Botany Downs would be far cheaper than a rail corridor.

Sir Barry last night condemned both that suggestion and the bus trial offer as "nutty", and accused the regional council of disrupting a long-proposed and vital public work "that must not be disrupted in any circumstances."

"I have to tell you I am disturbed by what appears to be an anti-rail sentiment on the part of the ARC," Sir Barry said.

"This is an integral part of the rail system. The attitude being displayed by the ARC is simply going to obstruct the creation of a vital rail link to serve what is the second largest commercial node in the Auckland region.

"It's almost as if they are treating Manukau as a poor relation in the Auckland region, and we are not going to be treated that way - commitments have been made to this city, not only through the regional land transport strategy but by central Government."

Sir Barry said a business case for the link was established several years ago when the former funding agency Infrastructure Auckland granted $6.5 million for enabling earthworks, to which his council voted to add $4.5 million.

That work had become urgent, as it had to be done in conjunction with the $174 million motorway link between Manukau and the western ring route, for which Transit New Zealand is about to award a contract.

He said the southern rail line was enjoying a huge growth in patronage, and the Howick to Wiri growth corridor was due for an influx of 40,000 more people in the next decade, all within "spitting distance" of central Manukau and a proposed underground train station.

This would eventually be fed by a rail link running down the centre of Te Irirangi Drive, which Manukau and the Government had built for $45 million with a 10m-wide rapid-transit corridor, and looping back to Panmure.

Although keen on a well-located free bus trial, Sir Barry said the rail route was the wrong place, as it would mean commuters arriving by bus from eastern suburbs would have to transfer to another bus, and then to a train at Wiri station.