Britain doesn't have the people and resources to deal with a "hard Brexit", according to a leading challenger to the British government's exit plan from the European Union.

"There are forty complex years of legislation that we will have to consider while establishing a new relation with the EU," Gina Miller, an investment fund manager, told Xinhua in a recent interview.

"Even if we are going to have a transitional arrangement, the complexity of the challenge is enormous, everybody have the experience of joining the EU while what is lacking is the 'leaving' process," she said, adding, "there are a lot of unknown questions."