First day nerves got to Paula Sherriff. Looking around at her Labour colleagues from the 2015 parliamentary intake, the new MP for Dewsbury in West Yorkshire saw former special advisers and academic high-fliers with Oxbridge degrees.

“I’d never been to university, so I felt completely out of my depth,” sighs Sherriff. “But then you find your way, you find your place. I’ll never be an expert in economics, but if you want somebody to get something through then I’m probably your girl because I’ve got this incredible northern grit.”

The 41-year-old former Unison shop steward found her way pretty quickly and has become one of the breakout stars of the 2015 cohort.

Last week, the Guardian revealed that Tesco had pledged to reduce the price of women’s twin-blade razors to the same as men’s at 50p for a pack of five following Sherriff’s pressure on the supermarket giant.

Kari Daniels, Tesco’s commercial director, wrote to Sherriff to insist the products were not simply a different colour – pink rather than blue – but added that Britain’s biggest supermarket would act “on concerns about the difference in price”.

Tesco’s concession is already being viewed as one of the major victories in the war to end gender price discrimination on the high street. The news added just a little extra lustre to a short but glittering parliamentary CV that includes: persuading Boots to pilot a scheme to let customers gift sanitary products to food banks; forcing WH Smith to lower product prices in hospital shops to match those in high street stores; and making House of Commons history in her bid to abolish the so-called tampon tax.

Sherriff joined the police at 18 and then spent 13 years in healthcare, but, as an MP she is defining herself as the champion of the shopper. She tweeted after the Tesco story broke:

Her efforts in highlighting gender price discrimination in clothes, beauty products and toys during a parliamentary debate, secured in her name last February, were noted by Jeremy Corbyn. Sherriff did not vote for him in either of his leadership election victories – she backed Yvette Cooper in 2015 and then Owen Smith last summer – but he still made her Labour’s women and equalities spokeswoman in October’s reshuffle.

Fresh off her Tesco triumph, Sherriff will now push supermarkets and major brands to sign up to a charter pledging not to “knowingly impose” prices that rip-off women. Analysis suggests that products aimed at women are, on average, 37% more expensive than identical items marketed to men.

“It’s time just to raise an awareness among retailers about the ‘pink tax’ or the ‘sexist surcharge’ or whatever you want to call it,” says Sherriff. “I just like the idea of asking them to not just talk about specific items but to sign up to this mentality. I just like the idea of shops saying: ‘We do not impose a sexist surcharge.’”

This month Sherriff will meet executives at Proctor & Gamble, which manufactures the Tampax and Always feminine hygiene brands, to talk about how it can help with The Homeless Period Campaign by donating sanitary products to shelters. An online petition aimed at P&G gathered nearly 70,000 signatures.

This follows Sherriff’s success over the Tampon Tax last year, when she became the first opposition MP to amend a government’s budget. Sherriff was furious that tampons carry 5% VAT – or “vagina added tax” as she memorably described it to the House of Commons – because of European Union rules.

At a birthday party for Clive Lewis, who is now shadow business secretary, Sherriff told senior party aide Nick Parrott that she was desperate to remove the rate altogether. Parrott devised a “long-shot” plan that allowed Sherriff two attempts at forcing the government to accept a zero rate.

After narrowly losing the first time around, Parrott and Sherriff ambushed the government by making a Faustian pact with a group of Conservative Brexiters to sign an amendment to abolish VAT on tampons. This was tabled shortly before the finance bill debate took place, so that the Conservative whips had no time to persuade rebels to change their minds.

The government had to adopt the amendment or face humiliating defeat. David Cameron headed to Brussels, where the UK and other EU members states were granted permission to abolish VAT on sanitary products.

“All the major retailers have agreed in writing that they will pass the savings on to the consumer,” says Sherriff, proudly.

Prior to this nugget of Commons’ history, Sherriff had already forced WH Smith to drop its prices in hospital shops. As a junior manager responsible for outpatient services in Wakefield, Pontefract and Dewsbury, Sherriff found out how chains would sell their products at a premium in hospitals. For example, people were paying 89p more for a bottle of water in a WH Smith shop in a Wakefield hospital than they would in Leeds city centre.

WH Smith bowed to the pressure and lowered prices on items such as “get well soon” cards. Today, Sherriff is full of praise for the chain. “Stephen Clarke, who is the CEO, keeps in touch with me literally monthly, saying: ‘Look, if there are any problems, just let us know.’ It’s fantastic, all credit to them.”

By contrast, Marks & Spencer refused to yield on its higher prices in hospital outlets, arguing it was impossible because they are run under franchise and forcing cuts would breach competition law. But M&S had better heed her Twitter warning: the high Sherriff of shops is preparing to ride into town once more and she isn’t about to let any major retailer escape her sights.