* Poland investigating if confidential information leaked
* Allied Irish says no irregularities in process
* Irish finance minister: Proper procedures were followed
(Adds Allied Irish Banks, Irish minister comment)
DUBLIN/WARSAW, Sept 13 (Reuters) - Polish regulator KNF is to probe Spanish group Banco Santander's deal to buy Zachodni WBK, the Polish arm of Allied Irish Banks, to see if confidential information was exchanged.
Allied Irish Banks said suggestions of any irregularity were unfounded while Ireland's finance minister, Brian Lenihan, a minority shareholder in the Irish lender after a state bailout last year, defended the transparency of the sale process.
On Friday, Santander said it was to buy Allied Irish's 70 percent holding in BZ WBK for 2.9 billion euros ($3.7 billion), beating French bank BNP Paribas and PKO BP, Poland's top lender and backed by the government.
KNF spokeswoman Marta Chmielewska-Raclawska said: "There have been some concerns. So, as is normally the case, we will check whether confidential information, such as result forecasts, was not revealed to potential buyers as part of the negotiations".
Santander would not comment.
Allied Irish said: "The sales process which resulted in Banco Santander agreeing to buy AIB Group's majority stake in BZWBK was conducted in an entirely appropriate manner".
Lenihan told Reuters: "I am sure all the proper procedures had been followed. It is a demonstration of the confidence in Allied Irish and in the market that they got such a high sum. It is money that talks here."
KNF, the Polish securities and financial watchdog, will need to approve Santander's takeover of BZ WBK. Analysts expected the process to take several months.
KNF will consider Santander's financial condition in the context of Spain's economic situation, the spokeswoman said.
Santander, which has emerged as one of Europe's strongest banks after the financial crisis, said the purchase posed no risk to growth or tighter capital ratios under Basel III rules.
It has already said it would call a tender for the remaining BZ WBK shares, as required by Polish law.
The regulator said Santander's offer could not be lower than the 227 zlotys per share it agreed to pay Allied Irish.
BZ WBK shares closed 9.7 percent higher at 214 zlotys. (Reporting by Chris Borowski in Warsaw, Tracy Rucinski in Madrid, Andras Gergely in Dublin, and Carmel Crimmins in Galway, Ireland; Editing by David Cowell and Dan Lalor) ($1 = 0.7816 euro)