PLANS for a huge new dock on Southampton Water have been dealt a last-minute blow by the port's biggest container terminal shareholder.

Southampton Docks operator Associated British Ports wants to build a £750m container terminal at Dibden Bay.

It argued at a public inquiry, which ended in December, that it is vital to the city's economic future.

Shortly after that inquiry, another one began into an even bigger scheme on a former Shell oil refinery site on the Thames Estuary and it is due to end on Friday.

The Thames scheme, known as London Gateway, is being promoted by P&O, which is the 51 per cent shareholder on Southampton Container Terminal - and Shell UK.

So far ABP, which has a 49 per cent stake in Southampton terminal, has insisted that the main justification for Dibden Bay is that it is "necessary to secure the future of the port of Southampton itself" and is not an alternative.

But if Transport Minister Alistair Darling decides the issue comes down to national interest and he has to choose between Dibden or Gateway, P&O has sent in a comparison on the two developments.

On the environmental front, it says the Bay would "have a direct impact on up to 115 hectares of designated Special Protection Area", while London Gateway would mean no loss of SPA.

Dibden Bay, it says, is also a designated Site of Special Scientific interest while, it adds, "no works at London Gateway Port are within either an SSSI or a proposed SSSI." In terms of ability to meet the national container demand, Gateway could handle 3.5 million twenty-foot containers, compared with Dibden's 2.1 million.

Gateway, it says, could meet UK need beyond 2020, whereas the Bay could only meet demand until 2016.

Meanwhile, the P&O move has been welcomed by Residents Against Dibden Bay Port chairman Paul Vickers.