A former cabinet minister helped to lobby the government to seek contracts for a multinational firm he is paid to advise.

Owen Paterson, a former environment secretary and leading pro-Brexit campaigner, is paid nearly £100,000 a year by Randox, a private forensic testing firm, to act as a consultant.

Whitehall documents obtained by the Guardian show that Paterson and Randox lobbied the Department for International Development to secure contracts from the department.

Paterson, the MP for North Shropshire, faces the possibility that he may have broken parliamentary rules on lobbying. Asked to comment, he said: “My financial interests have been correctly declared according to the rules of the House of Commons.”

The rules state an MP may lobby on behalf of a paying client, but there are restrictions. Any lobbying must not help to give an exclusive financial benefit to the client, and the client must not have initiated the lobbying.

According to the documents, which were released under the Freedom of Information Act, Randox wrote in July 2016 to Priti Patel, then the international development secretary, asking for a meeting.

Randox wanted to discuss the “healthcare diagnostics services available” from the firm and outlined the advantages of its products, according to the documents.

Paterson and a representative of Randox held a meeting with Rory Stewart, then the junior DfID minister, and DfID officials in January 2017.

A DfID note of the meeting recorded: “This meeting covered Randox’s laboratory quality assurance systems, DfID’s broad approach in health, and DfID procurement routes and potential commercial opportunities that Randox may wish to explore.”

The note added: “DfID does not currently fund Randox directly or as a major subcontractor. DfID support for health does not typically include direct funding for the laboratory equipment, or associated quality assurance products and services that Randox provides.

“Although we do not have immediate funding opportunities, we are helping connect Randox – as a British company with a strong shared interest in improving quality of healthcare in developing countries – with other potential commercial opportunities they may wish to bid for.”

According to the note, Stewart later sent Randox contacts for other UK and foreign government organisations that could award them contracts. The firm has more than 1,300 employees and says it sells its products to 145 countries.

Paterson, who was the environment secretary between 2012 and 2014, started working as a paid consultant for Randox, which is based in County Antrim, in August 2015. At first his annual fee was £49,000. This was doubled in 2017.

According to the parliamentary code of conduct, MPs can take part in lobbying for a client provided that “their approach or participation does not seek to confer benefit exclusively on that person or organisation (or on their client) and provided that that person or organisation (or their client) has not initiated the event”.

MPs are barred from initiating an approach to a minister to lobby to gain a financial benefit for a client.

It is not known who wrote the initial letter to Patel in 2016 requesting a meeting for Randox. Neither Paterson nor Randox responded to questions from the Guardian asking who wrote the letter. DfID said the “author of the letter does not want his name put out in the public domain, and to do so would breach the general data protection regulation and the Data Protection Act”.

A spokesperson for Randox said: “It is a matter of public record that Owen Paterson has worked for Randox Laboratories Ltd since August 2015. We have no further comment to make.”

DfID said it had not awarded any contracts to Randox since the firm asked for the meeting in July 2016.

Paterson has faced criticism that unknown donors have funded nearly £39,000 of his trips by routing the funds through his personal thinktank, UK 2020. The thinktank has been used to pay for 10 trips.

MPs are required to declare the source of funds for any overseas visit worth more than £300. As a private company, however UK 2020, is not required to identify its donors. By citing his thinktank as the source of funds, Paterson has effectively avoided revealing who financed them. Paterson said he had declared all required information in his register of interests.

Randox has been mired in controversy over claims that scientists manipulated forensics data, leading to the quashing of convictions. Randox says that since acting as whistleblower, it has fully supported a police investigation into the claims.