The plans are being worked on by Kate Barker's Treasury-sponsored review on the undersupply of housing, which is due to report next month.
However, planning minister Keith Hill has announced the plans now so that they can be added to the planning bill, currently being read in parliament.
Hill emphasised that the government was hoping to persuade developers that the tax would be better than the existing system.
He said: "It will give developers a choice. If they wish to negotiate a traditional section 106 agreement then they can. But if they want greater speed and certainty they can pay the charge."
A Housebuilders Federation spokesperson said the move would not improve the system. "If the tariff is too high then the developer will exercise his right to a negotiated settlement, which will bring us back to square one," he said.
One housing specialist was also sceptical of the new flat rate system.
He said: "The tax and the alternative amount to little short of a tax on betterment, with all pretence that the payments are necessary to release the development abandoned."