Boulger reckoned that while Corbyn and McDonnell will take Labour voters from the Green Party and the Scottish National Party it will lose the support of political moderates.
Corbyn’s policies include charging a higher rate of corporation tax – something Boulger claimed could drive international corporations out of the UK should he become Prime Minister.
He would also consider starting a right to buy equity scheme for private sector, a plan which was branded “disastrous” by a mortgage broker last month.
McDonnell’s radical ideas have in the past included nationalising banks and forcing them to invest directly in the UK economy.
Boulger said: “Corbyn’s appointment is going to push the Labour Party a long way to the left – it’s very much in soft communist territory.
“The fact that he’s chosen McDonnell to be shadow chancellor will make it much more obvious what Labour will stand for over the next few years.
“In the most important cabinet post from an economic point of view he’s appointed someone whose views are aligned with his but from an electoral perspective it weakens the credibility of Labour.
“People on the soft left and the hard left will give him support; there will be people who might have voted green or SNP in Scotland who will be attracted, but what he needs to do to get into power is attract people in the middle.”
Corbyn’s appointment has divided Labour, as fellow leadership candidates Yvette Cooper and Liz Kendall as well as Chuka Umunna, Mary Creagh, Tristram Hunt, Rachel Reeves, Chris Leslie, Jamie Reed, Emma Reynolds, Shabana Mahmood and Caroline Flint ruled out serving in Corbyn's shadow cabinet.
Boulger said: “If Corbyn was Prime Minister there would be a danger of international corporations leaving the UK If he increased company tax significantly.
“One of the reasons people position themselves in UK is they deem it a fair political system.”
But Jonathan Burridge, a mortgage broker based in East London, welcomed Corbyn’s appointment to stimulate debate.
He said: “All of the pundits have got it wrong – perhaps the time is right for a change in politics and perhaps he represents it.
“I can’t imagine that the man will be the leader of the country but Labour was once the opposition in the House of Commons and that hasn’t been the case lately.
“The Conservatives need some opposition. The closest we’ve got is the SNP at the moment.
“It will be interesting to see how this man and his unique stance changes things.
“I’ve long believed that our government is run by professional politicians rather than people who want to make a change but you can’t say that about Corbyn.”
Burridge said some of Corbyn’s ideas are sensible, such as nationalising energy firms.
He added: “Energy should be nationalised – that should be a right for every individual in a first world nation.
“I find the idea of people not being able to put their lights on in winter particularly abhorrent.”
However Burridge agreed with Boulger that Labour won’t capture the voice of the average Brit in the next few years.
He said: “I can’t see a Labour Party forming the next government because they are so off the mark on what represents the voice of Britain and that was shown in the election.
“Unless the current government makes an utter pig’s ear of things I can’t see Labour offering a sensible alternative.”