London, Jan 8 : UK Prime Minister Boris Johnson said that the easing of England's new national lockdown, the third of its kind since the onset of the pandemic early last year, will be a "gradual unwrapping" and not a "big bang". Addressing MPs in the House of Commons, Johnson said that the government will use "every available second" of the lockdown to place an "invisible shield" around the elderly and other vulnerable people through the rollout of Covid-19 vaccines in the coming weeks, reports Xinhua news agency. The Prime Minister justified his decision to order a third national shutdown with the emergence of a new variant of the virus first identified in Britain, which is said to be up to 70 per cent more transmissible. The variant was "spreading with frightening ease and speed in spite of the sterling work of the British public", said Johnson, adding that it left him with "no choice" but to implement the third lockdown in England. "This mutation has led to more cases than we've seen ever before. Numbers that alas cannot be explained away by the meteoric rise in testing," Johnson told MPs. "When the ONS (Office for National Statistics) reports that more than 2 per cent of the population is now infected and when the number of patients in hospitals in England is now 40 per cent higher than the first peak in April it is inescapable that the facts are changing and we must change our response." Announcing the lockdown on Monday evening in a televised address, Johnson urged people across the country to "stay at home" except for permitted reasons, echoing the message back in March 2020. The House of Commons was recalled on Wednesday from its Christmas recess to debate and retrospectively vote on the lockdown which has already been in force. It has the backing of the main opposition Labour Party. The Prime Minister has also pledged that his government would "do everything we can to keep the virus under control", warning that there are "tough, tough" weeks ahead in the fight against the pandemic. /IANS