The GDS, the first of the banks' to be published this quarter, shows that loans secured by residential mortgages stood at $24.93 billion at December 31 compared with $24.32 billion at the end of September.

Using Reserve Bank figures as a proxy for the market, that puts BNZ's share of the market at 17%, unchanged from September 30. (The actual figures from all the mortgage-lending banks, which won't be available for the December quarter until all banks have published their GDS's, put BNZ's market share slightly lower at 16.85% in September.)

In the September quarter, BNZ reclassified a large number of business loans which are secured by residential property after beefing up its reporting systems.

BNZ has said it would prefer the figure for housing loans in note 10 of its latest accounts, $23.39 billion compared with $22.91 million at September 30 (which was note 13 in its September GDS) be used to calculate its share of the mortgage market.

However, the accounts of the other home lending banks don't include directly comparable figures. By contrast, all of the banks are required to disclose loans secured by residential mortgages. All banks have always been entitled to include business loans secured by residential mortgages in that category.

Banks have to provide only 50% of the minimum 8% capital backing for housing loans compared with 100% for business loans.