The bank has also warned two Muslim organisations, including a mosque, that their accounts will be terminated in 60 days.
A major retail bank is to terminate the personal accounts of an entire family, including that of a twelve year old, giving four people 60 days – and no explanation – to find an alternative bank.
The family has also received similar letters about account closures for their business accounts.
Anas Altikriti, an outspoken pro-Palestinian commentator, told BuzzFeed that each member of his family (himself, his wife and his two children, one 12 and another 16) received an identical letter on the same day stating that their bank accounts would be closed.
The letter said: "After a review of your relationship with HSBC, we have taken the decision that we no longer wish to provide you banking facilities and are closing your accounts."
It also asked the four individuals "not to approach them regarding any kind of explanation because they are not going to give us any and not to approach them or apply to re-open any accounts with either them or any of their affiliated," according to Altikriti.
HSBC told the BBC that race or religion played no part in any decision to close down any customers' account.
"We do not discuss relationships we may or may not have with a customer, nor confirm whether an individual or business is, or has been a customer.
"Discrimination against customers on grounds of race or religion is immoral, unacceptable and illegal, and HSBC has comprehensive rules and policies in place to ensure race or religion are never factors in banking decisions."
The next day, Altikriti received a letter about The Cordoba Foundation, of which he is the CEO. Two days later, his wife received a letter warning her that the account for Brighter PR, a company where she is a director, would also be terminated.
The Cordoba Foundation is a public relations, research and think tank dedicated towards fostering relations between the West and "the Muslim World", according to its website. The letter sent to the company by HSBC was worded differently, adding that an HSBC review of its customers found the Cordoba Foundation "falls outside of its risk appetite."
David Cameron in 2008 called the Cordoba Foundation "a front for the Muslim Brotherhood" when he was leader of the opposition and although Altikriti's father was head of the Egyptian political organisation, Anas Altikriti has denies he is a member of the Egyptian political organisation. He is however well-known for his criticism of the July 2013 coup against Mohamed Morsi, the former president of Egypt.
In April this year, the prime minister ordered an internal review of the Muslim Brotherhood's alleged links to terrorism.
Altikriti, the former head of the Stop the War coalition, which spearheaded protests against the 2003 invasion of Iraq, said he has contacted HSBC multiple times but has been told that he cannot be given an explanation. One customer service representative told him that she could see a decision has been taken to close his accounts but there was no explanation for why. He received similar responses when he showed the letter to his local branch.