The loans are said to have led to HBOS losses of ú250m
A BBC News investigation has uncovered alleged lending irregularities at HBOS, the bank now owned by Lloyds.
File on 4 has heard from firms that claim they were ruined by the actions of a senior executive, and management consultants recommended by the bank.
The bank and management consultants Quayside Corporate Services have denied any wrongdoing.
The loans from HBOS's "high risk" unit between 2002 and 2007 are said to have led to losses at the bank of £250m.
The unit was based in Reading, Berkshire.
File on 4 heard from businesses alleging that a bank executive, Lynden Scourfield, required them to employ consultants Quayside Corporate Services as a condition for getting a loan.
Nikki and Paul Turner, whose music production and publishing business needed loan finance from HBOS, claimed the business suffered as a result of the involvement with Lynden Scourfield and Quayside and are currently facing eviction from their home by the bank. Their account of events is strongly disputed by the bank and Quayside.
The Turners' MP, James Paice, told File on 4 that HBOS's new owners Lloyds were not taking seriously their complaints and those of other businesses.
Mr Paice said that a number of businesses ended up in more debt than before Quayside got involved.
He said: "The whole thing stinks.
"The contention that I and my colleagues have is that the bank or some of the bank's then officials were significantly party to allowing or indeed encouraging these businesses to get into greater difficulty than they may or may not have been in the first place
they flatly refuse [to accept] that."
Mr Paice has secured a Commons debate next Tuesday.
Lib Dem Treasury spokesman Vince Cable said: "If half of what I hear is true this is a very, very serious matter."
Mr Cable has called on the Financial Services Authority to investigate evidence of "very, very serious allegations".
'Fair and responsible'
Mr Scourfield refused to comment.
David Mills, who founded Quayside, denied any wrongdoing and said: "I and Quayside Corporate Services acted as advisers to a number of banks and accounting firms to help implement commercial decisions made by our clients to try to turn around failing businesses.
"I always kept the banks fully informed of progress with the businesses. Unfortunately, in a number of cases, companies were unable to pay off large debts incurred before Quayside Corporate Services' involvement."
MPs have criticised Lloyds Banking Group for not properly investigating business customers' complaints.
No-one from the group would be interviewed but in a statement it told the BBC: "We simply cannot comment on individual circumstances. However, we strongly believe that we have acted throughout in a fair and responsible way.
"Bank of Scotland deals in a sensitive and fair way with all of its corporate banking customers, including those experiencing difficulties. We stand by our customers and support them closely in managing their financial difficulties."