David Cameron's general election pledge of a law banning the Government from putting up income tax before 2020 was devised "on the hoof", one of his advisers has said.
Ameet Gill, who was responsible for events planning in No 10 under Mr Cameron, said the so-called five-year "tax lock" was "probably the dumbest economic policy" possible.
"Sometimes when a vacuum is there, it makes the government do some stupid things," he told BBC Radio 4's Week In Westminster.
"When I was in government, we made some announcements on the hoof just to fill that vacuum.
"Towards the end of the general election campaign in 2015, we did the five-year tax lock. It's when we committed to put in legislation that we would not increase taxes.
"It was probably the dumbest economic policy that anyone could make, but we kind of cooked it up on the hoof a couple of days before, because we had a hole in the grid and we needed to fill it."
Following the election the tax lock, which also covers VAT and national insurance, was passed into law and can only be overturned by a vote of Parliament.