During the leadership campaign, Corbyn often drew huge crowds at his rallys with his anti-austerity message and unconventional style of politics.
Yesterday Mr McNicol said that he wanted to see new Labour supporters “out on the doorsteps, alongside the members who’ve campaigned for years, or even decades”.
“A warm welcome to the 15,500 who have joined in the last 24 hours,” he wrote on Twitter.
Meanwhile Labour’s new deputy leader Tom Watson said that he hoped many of the ‘registered supporters’ who paid £3 to vote in the leadership campaign would now upgrade to full membership.
“I hope they can come with us on the journey to the election in 2020,” he told BBC1’s Andrew Marr Show.
“Let’s get these new members involved in campaigning, helping relay our roots in communities, being involved in a digital revolution in the party that allows members to feel that they’re more included in the decisions we make.
“We want them to be part of that and I don’t think anyone is disagreeing with that,” he said – ruling out any move to convert them automatically on grounds of practicality and cost.
Labour’s membership also rose significantly in 2010 when Ed Miliband became leader, but slipped back before reforms to the party’s structures last year.