The former Northern Ireland secretary Julian Smith is facing scrutiny for earning £144,000 a year from companies with close links to the region.

The Conservative MP for Skipton and Ripon earns up to £3,000 per hour as an “external adviser” offering guidance on “business development” for a hydrogen company owned by a Tory donor who also runs a Northern Irish bus factory.

The register of members interests shows Smith also works with a cruise ship refurbisher based in Newry, County Down, and the UK subsidiary of an Irish offshore wind company that is exploring an expansion to Northern Ireland.

All three of Smith’s extra jobs were approved by the Advisory Committee on Business Appointments (Acoba), the parliamentary watchdog that polices the commercial interests of MPs and civil servants.

Acoba put several conditions on its approval, including that Smith would not lobby or have any contact with ministers and government departments in connection with his clients. There is no suggestion Smith has breached any parliamentary rules.

But campaigners and other MPs have raised concerns, saying Acoba’s approval of Smith’s consultancies “beggars belief”, and existing rules needed to be “significantly tightened”.

Parliament’s committee on standards, which advises the prime minister on ethics in public life, is considering recommending a bar on MPs having second jobs as political or parliamentary consultants, following the scandal surrounding the MP Owen Paterson.

Paterson, another former Northern Ireland secretary, said he would leave the Commons after criticism of his “egregious” lobbying on behalf of two Northern Irish businesses.

Smith, a former chief whip, held the Northern Ireland brief from July 2019 to February 2020, helping restore the power-sharing agreement after a three-year deadlock. Just a few months after being sacked by Boris Johnson, he began accepting paid advisory work for companies connected to the region.

Since August 2020, Smith has declared payments £60,000 a year for 20 hours’ work – equivalent to £3,000 per hour – by Ryse Hydrogen, now renamed Hygen Energy. The company is owned by Jo Bamford, an heir to the JCB digger-making fortune who has donated £75,000 to the Conservatives. The Bamford family and its companies have given £8.7m to the Tories since 2002.

Bamford is also the owner of the Bamford Bus Company, which took over the Northern Irish bus-maker Wrightbus in October 2019, months after Smith started work as Northern Ireland secretary. Smith has declared that he had a meeting with Bamford in January 2020, while still a minister, to discuss growth plans for Wrightbus.

Wrightbus has contracts worth £12m and £66m respectively with Transport for London and Northern Ireland’s Department for Infrastructure.

Since March, Smith has also been employed at a rate of £60,000 for 30-40 hours’ work by the Newry cruise ship refurbisher MJM Marine. The company was briefly linked with a purchase of the struggling Belfast shipyard Harland & Wolff, although MJM Marine reportedly dropped its interest shortly before Smith started his role.

Since January, Smith has been collecting £2,000 a month to advise Simply Blue Management (UK), a subsidiary of the Irish offshore wind company Simply Blue. A spokesperson for the company, which already has projects in the Celtic Sea and Scotland, confirmed it was exploring expansion to Northern Ireland. Its two founders incorporated Simply Blue Energy (NI) in June.

Richard Burgon, a Labour MP who is proposing a private members bill to ban second jobs for parliamentarians, said: “When MPs are getting huge sums like this for a few hours’ work the public will rightly ask themselves in whose interest are these MPs really working? It beggars belief that this was permitted and it should be urgently reviewed.

“There is a simple way of preventing anything like this from happening again which is to ban MPs from having second jobs.”

Tom Brake, a former Liberal Democrat MP and the director of the Unlock Democracy campaign group, said: “Acoba approved these roles with indecent haste and conditions that will be very hard to monitor. Who is the fly on the wall to verify whether MPs refrain from lobbying the government or using information obtained in government?

“The rules need to be changed to create a real firewall between ministers’ experience and their ability to use their knowledge and expertise to influence government. Nothing less than five years will do.”

Stephen Farry, an MP for Northern Ireland’s Alliance party, said the regulations on MPs’ second jobs needed reform. He said the party “believes in the highest standards around openness, transparency and good governance. We believe the rules on outside work need to be significantly tightened and look forward to engaging with that process.”

Smith did not respond to a request for comment.

Bamford’s companies and MJM Marine were approached for comment. Simply Blue declined to comment.