Switzerland's central bank was embroiled in an insider trading scandal after bank chief Philipp Hildebrand was accused of speculating on currency transactions only weeks before he instituted dramatic policy changes that shifted prices in his favour.

The accusations, which have rocked the Swiss banking industry, were made by Swiss weekly newspaper Die Weltwoche in a statement before its Thursday publication. It said that previous reports that Hildebrand's wife was responsible for the foreign exchange transactions were misplaced and it was the bank chief who was behind the purchase and selling of currency that triggered an investigation by the Swiss National Bank (SNB).

The bank chairman also made several other dollar and euro transactions on the foreign exchange market between March and October last year, according to Die Weltwoche, which is close to the far-right Swiss People's Party (SVP).

Hildebrand has come under sustained attack from the SVP and its vice-president Christoph Blocher following the bank chief's efforts to bring down the value of the Swiss franc against the dollar and the euro.

The SNB shocked foreign exchange markets last September when it imposed a cap on the value of the franc against the euro to stop the currency soaring and thereby hurting Swiss exporters' earnings.

The Swiss weekly claimed that in March alone, Hildebrand bought US dollars worth SFr1.1m, saying it had access to extracts from the Hildebrands' banking documents. The SNB refused to comment.

The bank that allegedly handled the transactions, Banque Sarasin, said an employee had leaked client information by transmitting banking details to a lawyer close to the SVP. It said the member of staff had left the bank and could face prosecution.

Die Weltwoche said the same employee had lodged a complaint against Hildebrand for alleged insider trading. "We have all the bank statements showing the relevant transactions, plus a verbal assurance from a bank employee confirming that it was Hildebrand personally – not his wife – who ordered the transactions," Die Weltwoche's deputy editor-in-chief, Philipp Gut, told the Associated Press in a telephone interview on Wednesday.

According to the newspaper, Hildebrand bought more than $500,000 in two transactions dated 15 August, which he then resold in September – making a profit of SFr75,000 (£52,000).

On 15 August the dollar was worth 0.79 francs, against 0.92 francs on 4 October.

"It's a classic forex [foreign exchange] speculation," Gut said. "The only option for Hildebrand is to step down."

The Zurich-based weekly said it had obtained bank statements showing that he was the one who had bought large amounts of dollars before selling them at a profit.

The central bank said in December that an independent investigation into the Hildebrand couple's transactions found they complied with previously agreed ethical standards.

The probe was reportedly launched after SVP figurehead Christoph Blocher went to then president Micheline Calmy-Rey with extracts of banking documents.

Blocher, a billionaire, has so far refused to comment. A critic of SNB policy under Hildebrand, he is also a defender of Switzerland's banking secrecy laws.

Three weeks earlier the bank chief's wife, Kashya Hildebrand, who runs an art gallery in Zurich, said she bought dollars due to the fact that they had "hit a very low level and become ridiculously cheap".

In a written statement to SF, the Swiss television network, Hildebrand said she had always followed the foreign exchange market and had worked in the banking sector for 15 years between 1984 and 1999 before moving into art.