Portsmouth City Council has agreed that a stretch of land leading to the site near Fort Cumberland, Eastney, can be used as a road.
It comes after city lawyers warned the council that it could face a costly legal battle unless it gave permission to change the use of the land.
Cllr Mike Hancock, in charge of planning, regeneration and economic development, said: 'I resent the fact that we are being put in this position, but I do not think it will be of benefit to the taxpayer to risk tens of thousands of pounds of their money.
'I don't think we can afford to take that chance when all the advice says the courts will be against us.
'But one thing I cannot stand is someone putting a gun to my head and saying "I'll take you to court if you don't do this".'
At a cabinet meeting this week councillors grudgingly reversed their previous decision to block the road plan and agreed the land could be transferred from the planning department to the highways department.
Developer QinetiQ needs to provide the access road to fulfil conditions of its outline planning permission.
It means the firm can press on with a full planning application for 131 flats overlooking the beach at Fort Cumberland.
As well as finalising details of the access road, an environmental study is under way to see if the development would jeopardise a rare bird, the Dartford warbler.
Cllr Leo Madden said: 'This matter will go before the planning committee and it is best if these issues, the environmental impact and other issues, are taken up at that stage.'
Cabinet members Jason Fazackarley and John Ireland voted against allowing QinetiQ to use the land as a road.
Cllr Fazackarley said: 'I don't agree with the way QinetiQ have conducted their business and I don't want to be bullied by them on this issue.'