Labour is demanding an investigation into allegations that Priti Patel breached the ministerial code of conduct by lobbying fellow ministers over a PPE contract for a Tory donor and former adviser.

Deputy leader Angela Rayner and shadow home secretary Nick Thomas-Symonds wrote to the cabinet secretary Simon Case asking him to investigate what they described as a “glaring and flagrant breach” of the code.

Documents obtained by the Daily Mail show that the home secretary wrote to cabinet colleague Michael Gove after being contacted by a client of Samir Jassal over a £20m deal to supply personal protective equipment early in the coronavirus pandemic in April 2020.

Health secretary Matt Hancock responded that the masks being offered by Pharmaceuticals Direct Ltd were “not suitable for the NHS”. But the company was later awarded a £102.7m contract for a higher-specification face-covering.

PDL contacted Ms Patel for help with the cancelled £20m deal after an introduction from Mr Jassal, who previously worked as her adviser and has twice stood as a Conservative parliamentary candidate.

According to the papers obtained by the Mail, Ms Patel forwarded the letter to Mr Gove and said the potential loss of the order was putting PDL under “financial pressure”.

“I would be most grateful if you could review this matter urgently… and work with the company to distribute and supply these masks,” she wrote.

A reply from Mr Hancock said experts agreed the KN95 mask offered by PDL was not suitable for use in the NHS, but aded that he “appreciated”  the company’s efforts and had asked officials to liaise with them.

In July, PDL secured a £102.7m contract to supply the superior FPP3 masks, in a deal which is now being challenged in a High Court judicial review brought by the Good Law Project campaign group.

A spokesperson for Ms Patel said did nothing wrong: “The home secretary rightly followed up representations made to her about the vital supply of PPE.

“During a time of national crisis failure to do so would have been a dereliction of duty.”

But in their letter, Ms Rayner and Mr Thomas-Symonds said: “Given that the home secretary was introduced to PDL by her friend Mr Jassal, and the home secretary then immediately took it upon herself to lobby on PDL’s behalf, it is difficult to reach any conclusion other than that the home secretary lobbied the government on behalf of PDL as a favour to her friend, Samir Jassal.

“This would represent a glaring and flagrant breach of the Ministerial Code.”

They added: “The public has a right to know why the home secretary lobbied ministers on behalf of a client of Samir Jassal, her friend, former adviser and a prominent Conservative Party activist, candidate and donor.

“The public also has a right to know why the home secretary was demanding that huge amounts of taxpayers’ money was wasted on face masks that the Health and Safety Executive had found to be unsafe for use by frontline NHS staff, and why in the grips of the first wave of this awful pandemic the home secretary was spending her time lobbying to help her friends get rich quick rather than focusing on her job – securing our borders against the virus and working with police to keep our communities safe.

“This investigation must include not only the representations made by the home secretary on behalf of PDL in this instance, but also any further representations and any impact this or any other lobbying had on PDL being awarded a subsequent contract worth over £100m.”

The code governing government ministers’ conduct states that “ministers must ensure that no conflict arises, or could reasonably be perceived to arise, between their public duties and their private interests”.

The row comes months after Boris Johnson overturned the finding of his former ethics adviser that Ms Patel had breached the code by bullying staff at the Home Office, prompting the resignation of adviser Sir Alex Allan.

Good Law Project director Jolyon Maugham said: “Why did Jassal, a man connected to past and present Tory PMs, ministers and peers, reach out to Priti Patel for help?

“What was his role in winning the £103 million contract? What relationship did his connections with the party have to the £103 million contract won by Pharmaceuticals Direct?

“These are the questions at the heart of our judicial review of this most troubling of PPE contracts.”

Mr Jassal and PDL have been contacted for comment.