The first nationwide strike of its kind by workers from companies including McDonald’s, Wetherspoons and Uber has been hailed as a watershed moment in moves to organise in sectors where unions have struggled to take root.

A day of unprecedented action across eight British cities saw workers from the retail and hospitality sector take part in coordinated walk-outs supported by unions, campaign groups and the Labour party leadership, which instructed its MPs to join local picket lines.

The strike comes days after Amazon raised its minimum wage for UK and US workers in a major milestone for campaigners pushing for pay increases. However, the GMB union, which organises workers at the firm, has said the rise would be offset by the removal of employee share and incentive schemes.

The shadow chancellor, John McDonnell, addressed a rally on Thursday in Leicester Square, central London, and pledged that Labour in power would act swiftly to introduce a £10-an-hour minimum wage, one of the central demands of those taking part in the strikes.

“Our message to exploitative employers is that we are coming for you,” McDonnell said. He told Labour MPs that they had “a responsibility” to join picket lines in their constituencies. The grassroots Labour campaign group Momentum threw its weight behind the action, and organised pickets outside McDonald’s outlets across the country in support of workers calling for £10 an hour, an end to precarious contracts, and for their right to join a union.

In a day of action organised by War on Want, Unite and the Bakers, Food and Allied Workers’ Union, a broad demographic of strikers ranged from students and young workers from McDonald’s and Wetherspoons, through to couriers and drivers from largely BAME and immigrant backgrounds at Uber Eats and Deliveroo.

Pickets and demonstrations took place in cities including Bristol, Cardiff, Glasgow, Newcastle, Plymouth and Southampton, while Unite members at TGI Fridays restaurants in Milton Keynes and two in London staged their eighth walkout since the start of a row over a change in tips policy.

Those gathered in Leicester Square included striking Wetherspoons workers from its pubs in Brighton who had travelled to London after walking out at midnight.

The TUC general secretary, Frances O’Grady, described the strike as “small but growing”.

“These are often young workers who increasingly feel they have nothing to lose. They are on low pay, often without training and often on zero-hour contracts,” she said.

“Although these are small-scale actions, they are growing and spreading, and what I find really touching is that these are workers from different companies coming out to support each other.

“The key point is that a lot of these very rich and powerful multinational firms have deliberately put their workers on contracts that keep them scared. If you are on a zero-hours contract, they don’t have to sack you, they can just stop offering you shifts. So it’s a big ask to stick your head above the parapet.”

Workers at Uber Eats are asking to be paid £5 for each delivery and a further £1 per mile travelled during those deliveries. Last month, drivers staged a series of walkouts after the company reduced its minimum payment per delivery from £4.26 to £3.50.

The companies targeted by the strike action have defended the pay and conditions of their workers.

McDonald’s, which has taken issue with the widespread naming of the strike action on social media as “McStrike”, said that all of its restaurants remained open as usual despite what it described as “frustrating attempts by protesters at a handful of locations to impact our customers, and our restaurant teams”.

“This is the third attempt at action; and according to our records none of our people are on strike today,” the company added.

“Any suggestion this activity is widespread and growing is not accurate – fewer restaurants, fewer employees involved and less support for the union from our people. This is against a backdrop of more people choosing to join our business, with over 1,700 new employees since May.”

McDonald’s pledged to continue to offer a choice between fixed and flexible contracts, adding that its workers had told the company that they want to choose what works for them.

“Since offering the choice to our people 80% have made the decision to stay on a flexible contract.”

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A spokesman for TGI Fridays said: “Our team members are a part of our Fridays family. We believe they should be, and are, treated and paid fairly. Out of a workforce of over 5,500 team members, less than 1% are involved in this action.”

An Uber Eats spokesman said: “In response to feedback from couriers we’ve made some changes to our payment structure in London, which brings it into line with other cities. Our door is always open for individual couriers to speak to us about any issues they’re having.”

JD Wetherspoon said it had increased its spending on pay by £20m in the year to July, and would raise it by a further £27m this year.

The pub chain’s chairman, Tim Martin, said: “It is understandable that there is pressure on pay with low unemployment and a housing shortage. However, bonuses, free shares and other benefits should be taken into account in assessing pay. I don’t think it would benefit employees overall if, as some suggest, Wetherspoons ended bonuses, free shares and other benefits, and increased the basic rate of pay.

“It’s easy to be cynical about business, but companies like McDonald’s, TGI Fridays and thousands of other individuals and businesses make a big contribution to the economy and provide valuable work and experience for many people.”

Why I’m striking

Katie Southworth, 22, Wetherspoons in Brighton

Facebook Twitter Pinterest Katie Southworth, 22, works at Wetherspoons in Brighton and spends 80% of her wages on accommodation. Photograph: Alicia Canter/The Guardian

I’ve worked for Wetherspoons for the past two years in the bar and kitchen and continued after finishing my degree earlier this year. It’s quite a demanding job and you really do feel like you are put under a lot of time pressure.

I was demoted recently from being a shift leader to being a team leader. In the latter role I would typically earn about £8.85 an hour. At the moment though about 80% of my wages go on accommodation. Getting £10 an hour would give me the opportunity to live a fulfilling life. At the moment I have no hope of being able to live independently, get a mortgage or think of so many things that people take for granted. Even booking a holiday I have to give the pub six weeks’ notice and when I come back I have to be able to have enough money to pay my rent.

Boni Adeliyi, 21, TGI Fridays in Milton Keynes

Facebook Twitter Pinterest Boni Adeliyi, 21, from Milton Keynes, says £10 would make a major difference to her life. Photograph: Alicia Canter/The Guardian

I have been working for TGI Fridays (TGIFs) for about two and a half years, and while I am contracted 12 to 15 hours a week, I end up working about 25 to 30 hours a week. I also have two other jobs.

I’m taking part in the strike because £10 would make a major difference. It would allow me to focus on one job. At the moment I work days and nights. I will literally work at 10pm at TGIFs and nanny until 10 in the morning and then come back to TGIFs.

I wanted to study but the amount I was able to save basically halved when 40% of our credit card tips were moved to the back of house staff. I had to raise £19,000 in fees just for one year. It’s still not as much as I would like to raise but I am able to save it and I do work very hard.

I’ve been in self-employed jobs since the age of 13 but this is my first paid role of this kind, so when I joined Unite earlier this year it gave me a sense of safety and confidence which I never had before.

Lewis Baker, 25, McDonald’s in Crayford

Facebook Twitter Pinterest Lewis Baker, 27, works at McDonald’s in Crayford and joined the McStrike to fight for an end to youth employment rates. Photograph: Alicia Canter/The Guardian

I have worked at McDonald’s for about five years but it was some changes that came in under a new manager – cuts in shifts and extra pressure on people – which got me involved in a union.

Me and two other workers initially started to get involved in the union and put in about 15 grievances, which the company didn’t answer.

I earn about £250 a week but for me a big one is ending youth rates. Sixteen-year-olds at McDonald’s get a minimum, so really a big one for me is ending that differentiation.

I still struggle though. I do about four shifts a week and it’s quite a lot when you are trying to balance studies as well. If I was earning £10 an hour it would make a difference.

I don’t think we have reached a tipping point yet but obviously the action today is massive. I think that the more solidarity we have [the more it] is going to make a difference in the long run.

Even today I got a message on Twitter out of the blue from someone who is a pizza delivery driver from another company. He wanted to know how he could get involved and what he could do.

• This article was amended on 5 October 2018 to clarify remarks made by Boni Adeliyi about her working hours and the effect on her pay when 40% of credit card tips were moved to the back of house staff.