Calls have been made for a “full independent inquiry” to be held into whether a Scottish Tory MP broke the ministerial code over his wife’s stake in an oil giant.

Former Scotland Office minister David Duguid has been a stern critic of introducing a windfall tax on energy giants.

But it has been claimed that the Banff and Buchan MP did so during his time in government without declaring his wife’s £50,000 shares in energy giant BP.

Mr Duguid has previously voted against proposals to examine the impact of increasing taxes on energy companies and has spoken out against potential windfall taxes on four separate occasions since 2022.

SNP MP Tommy Sheppard has written to both the Cabinet Office and the Parliamentary Commissioner for Standards demanding “full transparency” on the issue.

Mr Sheppard said: “Serious questions must now be asked as to whether David Duguid broke the ministerial code by failing to declare his wife’s huge shares in BP.

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“This revelation underlines the argument that Scottish Tory MPs only have one interest, and that is their own personal gain.”

He added: “Would Mr Duguid have had the same desire to oppose a windfall tax on energy companies if he wasn’t set to profit from it? I highly doubt it.

“That is why a full, independent inquiry is essential to clarify if Mr Duguid has, indeed, broken the ministerial code. Full transparency is absolutely key in order to get to the bottom of this.”

Under the UK ministerial code, ministers must provide a list of all the interests held by themselves and close family members that could create a conflict of interests, including shares held under £70,000.

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It is then decided by the independent adviser of ministers’ interests whether the interest is determined as relevant enough to publish.

Since the beginning of 2022, the Conservative MP has criticised the idea of a windfall tax four times in the Commons and has voted against the proposals.

He was a minister in the UK Government from June 2020 until September 2021, before being appointed again by Liz Truss in October 2022.

His wife’s shares were not published in the list of ministers’ interests published by the Cabinet Office.

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BP’s shareholder register shows Mr Duguid stopped being a shareholder in November 2012, on the same day his wife joined the company’s register of members.

Analysis by the Guardian shows that as of today, Mr Duguid’s wife has more than 11,000 shares and will have received more than £2,000 last year in dividends.

Since the beginning of 2022, Mr Duguid has declared interests in BP in two parliamentary debates, but only by referencing his prior employment in the industry, and not his wife’s shares.

Mr Duguid is also vice-chair of the British offshore oil and gas industry all-party parliamentary group.

Mr Duguid's team has insisted that that the shareholdings were declared to the Cabinet Office as part of the process for declaring interests under the ministerial code.

A spokesperson for Mr Duguid said: “Mr Duguid followed the prevailing rules for reporting relevant financial interests.”