How would you feel if you were dumped by your bank with no explanation?

You’ve been a loyal customer for years, but then a letter arrives saying your bank has decided it will shut your accounts, and you will have to take your business elsewhere. No reason is given and the decision is final.

Guardian Money can reveal that the numbers of people being given the boot by their bank appear to have increased sharply. And Samuel (he didn’t want us to use his full name) is the latest person to be on the receiving end of this Kafkaesque treatment. Like many of those affected by this, he believes he is a victim of discrimination.

Samuel, a father of two preschool-age children who lives in Kent, contacted Money after NatWest told him he was being dumped. He’s been with the bank for more than 10 years, but it wrote to him on 12 January to say that it had, “with regret”, decided it would be closing his four personal accounts, plus the joint account he shares with his wife. The couple also have a NatWest mortgage, and the bank is “strongly recommending” that they give serious thought to moving it to another lender.

Samuel has been given 60 days to find a bank willing to take him on, though NatWest told him: “We will not be able to provide references for you.” In the meantime he must cut up and return his debit card.

So what, some will wonder, has Samuel done to merit being treated like a pariah? He told us he can’t think of any reason why the 71% taxpayer-owned bank is so keen to be shot of him, and says he and his family have been treated like “criminals”.

With the bank refusing to say anything about Samuel’s case, it’s hard to avoid concluding that NatWest, and some other banks, are dumping customers and organisations with links to countries about which they have concerns.

Samuel was born in Nigeria and moved to the UK more than a decade ago. His full name is unmistakably of African origin, though he hasn’t been back to Nigeria for more than eight years. Notably, NatWest is not closing the accounts held solely by Samuel’s wife, who was born in mainland Europe. Both have permanent residence cards from the Home Office.

In March 2015, Money reported how economics professor Iraj Hashi had had his NatWest current account, savings accounts and credit card shut down with no explanation. The only reason he could think of was that he was born in Iran.

Last April the Guardian related how a UK law firm was handling more than 60 complaints by Iranian nationals who had had their UK accounts closed. Meanwhile the Guardian’s sister paper the Observer last year reported on the case of Mohammad Rahman, who had his bank accounts frozen and then closed by Barclays.

You can perhaps see a theme here: many of those affected are of Asian or African origin. So what’s going on? Welcome to the secretive world of bank “de-risking”.

In 2016, City regulator the Financial Conduct Authority (FCA) revealed that in recent years it had become aware that banks were withdrawing banking facilities from customers – or failing to offer them in the first place – in greater numbers than before. It said there was a perception that this was driven by banks’ concerns about the money laundering and terrorist financing risks posed by certain types of customer.

A 2016 report commissioned by the FCA revealed that, between them, two large (unnamed) UK banks were closing about 1,000 personal and 600 business/corporate accounts per month for “risk appetite-type reasons”.

It also revealed that the Financial Ombudsman Service (FOS) was dealing with 20 to 30 complaints a week about bank account closures. However, when Money spoke to the FOS this week, it estimated that the figure was now nearer 80-90 a week.

It follows that because countries deemed risky in terms of money laundering and financing terrorism tend to be Asian and African, people from these areas may be particularly vulnerable.

Samuel did a master’s degree at a London university and now works full-time for a construction-related company, while his wife came to the UK about 15 years ago and has been a NatWest customer since about 2003.

Samuel says their nightmare began when his accounts, including their joint account, were frozen. He says they only discovered this when the family was out shopping and his card was declined.

After many calls and branch visits, they both received formal letters saying their accounts would be closed. Samuel’s letter states that following a review, the bank had “reached the conclusion that we will no longer provide these facilities for you”, adding: “We assure you we have only reached this decision after careful consideration; however, our decision is final and we are not prepared to enter into any discussion in relation to it.”

He said: “I don’t know how I will be able to go to another bank without a reference or explanation as to why my accounts have been closed … We strongly believe there is no tangible reason relating to any actions or fault of ours. I don’t have a criminal record or any history of fraud whatsoever. I’ve also got a very good credit history.” Samuel says it is wrong that banks have the power “to wreck innocent individuals’ and families’ lives”.

NatWest told us it can’t discuss Samuel’s case.

The numbers of people being ditched by their bank look set to rise even further because UK banks and building societies have this month started carrying out immigration checks on 70m personal current accounts as part of measures agreed by parliament to encourage those living and working in the UK illegally to leave. Action taken could include closing accounts.

But critics have warned of the possibility of errors and cases of mistaken identity.