The cash boost is welcome news to Ipswich officials and supporters, who are still celebrating the team's win over East Anglian rivals Norwich City on Sunday.
Existing boxholder Mr Britton is close to completing a move to buy 5% of shares in Ipswich Town plc for around £175,000 and purchase loan notes.
Meanwhile, Mr Spencer, whose personal wealth is estimated at £372million, has increased his shareholding in the Blues to 15%, the maximum allowable without the board needing permission from other shareholders.
Ms Bellingham, chair of medical insurance company Marketform, has taken her ownership of the club to around 13% after converting a significant amount of her £415,000 loan notes into shares. She joined the board two years ago, becoming the club's first female director.
Although Mr Britton and Mr Spencer have made the hefty investments, neither plans to join the board of directors at Portman Road.
Mr Spencer said: “David Sheepshanks and the board are doing a first class job in difficult circumstances.
“However, with the benefit of these funds and the long-term investment in the Academy, I have every hope the good times will soon be back at Portman Road.
“David and his fellow directors have again offered me a seat on the board but due to business pressures, I have declined as I'm confident that David and his fellow directors will represent my best interest.”
Town chairman David Sheepshanks last night confirmed the triple investment and said: “This is all tremendously good news for the club.
“Further new investment for which we are very appreciative, coupled with the rescheduling of our long-term debt puts us in an increasingly stronger position for the future.
“Spurred on by the much-improved form on the field, I'm excited about our future prospects and hope that all supporters will feel similarly encouraged.”
Mr Britton, who runs Britton Construction with his wife Jacqueline, a keen Town fan, is also a director of three other companies, Brook Farm management consultancy, Hereditable Development, which are both dormant companies, and Britton Engineering.
Although not a director, we understand Mr Britton has been subject to stringent checks by the Blues and vouchsafed by a senior member of the club's staff.
The Essex-based businessman is a supporter of his local charities and recently sponsored the Tour De Tendring, donating funds to the RNLI. He is also listed as a contributor to Conservative MP Bernard Jenkin's constituency party and was heavily involved in the building of the retail outlet complex at Little Clacton.
With homes in St Tropez, New York, London's Holland Park and Suffolk, Mr Spencer is a fixture in the Sunday Times' Rich List, earning a £5m bonus this year from the world's largest money-broking company Icap.
A known art-lover and keen yachtsman, Mr Spencer splashed out £1m for Robbie Williams to sing at his wife Lorraine's birthday party in St Tropez last year in front of 300 guests.
Ms Bellingham, who lives at Lavenham, is a keen Ipswich fan and attends as many matches as she can home and away, when not travelling to Australia, America and the Far East on business."
Source: The East Anglian Daily Times.