New Zealand's financial regulator is challenging a judge's decision that certain trades by Milford Asset Management's Mark Warminger didn't manipulate the market.

Warminger last month was found to have manipulated the market in specific trades of Fisher & Paykel Healthcare (FPH) and A2 Milk (ATM) shares.

While the Financial Markets Authority argued that 10 instances of Warminger's trading breached securities law, Chief High Court Judge Geoffrey Venning was satisfied that only those two sets did.

Warminger is challenging the findings against him and on Friday the FMA confirmed it would also cross-appeal on some of its causes of action which failed in the High Court.

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The regulator would not comment further.

Justice Venning said in his decision that Warminger breached the Securities Market Act "by manipulating the market for shares in FPH on 27 May 2014 by increasing the offer quote and price for FPH shares and maintaining them at a higher level than otherwise would have been the case and also by entering a crossing for the sale of FPH shares which created a misleading appearance as the price of the crossing was influenced by his earlier trades".

Justice Venning also declared that Warminger breached that same law "by manipulating the market for shares in ATM on 9 July 2014 by increasing the offer quote and price for ATM shares and maintaining them at a higher level than otherwise would have been the case and has also created a misleading appearance as to the demand and/or price for ATM shares on the day".

It has yet to be decided if Warminger is to pay a penalty and what any penalty would amount to. The maximum possible penalty is $1 million per trade.