National Australia Bank has delayed the float of Clydesdale Bank by 24 hours to update its listing prospectus after a request for more information from a rating agency. 

Clydesdale's shares were priced at 180 pence yesterday. The bank is headed by former AIB chief executive David Duffy. 

It has received a request from an unnamed rating agency that could result in a downgrade of the bank's deposit rating, NAB said. 

The rating could also be placed on credit watch. 

Investors will have another day to consider a revised IPO prospectus. 

The nearly 180-year-old British lender is expected to have a senior standalone investment grade credit rating, NAB said. 

Clydesdale shares were priced towards the lower end a wide 175-235 pence indicative range. 

Some analysts had considered the initial range "aspirational", given recent declines in share markets.

AB said today that the float was multiple times covered at 180 pence, but that it would announce a final pricing tomorrow. 

The Australian lender, which bought Clydesdale in 1987, is expected to sell 25% of the unit in the IPO and float the rest to its shareholders.