The following month, London's Conservative mayor, Boris Johnson, gave an interview to Channel 4 News endorsing the idea in terms almost identical to the Strangers into Citizens proposals. He said the expulsion of London's 400,000 illegal immigrants was "just not going to happen". While he was powerless to change national policy on the issue, Johnson said he wanted to "lead the debate" by commissioning a study into the feasibility of the idea. He said he favoured the idea of an "earned amnesty", whereby after a period of about five years individuals could "show their commitment to this society and to this economy" to earn the right to stay. "We want to look in detail at what the economic impact of such an earned amnesty system would be," he said.