Labour frontbenchers have defied the orders of Sir Keir Starmer not to appear on picket lines as rail workers launched the biggest strike in three decades.
Half of Britain's train lines are closing over the three-day walkout, with many running at just 60% of usual service on the interim days.
Overall it is expected just one in five normal trains will run while the workers are on strike.
The Labour leader banned his top team from appearing on picket lines, and in a leaked memo were told to “show leadership” by Starmer’s office.
It added: “And to that end, please be reminded that frontbenchers including [parliamentary private secretaries] should not be on the picket lines.
“Please speak to all the members of your team to remind them of this and confirm with me that you have done so.”
But despite the memo, a number were seen taking up signs anyway in solidarity with workers.
Labour's Whip Navendu Mishra posted a picture saying: "This treacherous government has underfunded & mismanaged our public transport network for over a decade.
"As a proud trade unionist, I stand with all workers on our railway network who are taking industrial action to fight for their jobs & keep passengers safe."
Paula Barker, the Labour MP for Liverpool Wavertree and a Parliamentary Private Secretary (PPS) in the opposition defence team, joined him.
She tweeted: “Proud to support the workers on the picket line at London Victoria this morning, alongside colleagues. These workers keep our country moving safely 365 days a year. The least they deserve is to be paid properly and feel secure in their jobs.”
Shadow Environment Secretary Alex Sobel joined workers on strike at Tottenham Court station in London,
Jarrow MP Kate Osborne tweeted: "On the picket line at Bromley. I'm a trade unionist, I will always stand on the side of the workers. Solidarity."
The Rail, Maritime and Transport union called for a 7% pay rise to keep up with the increased cost of living, as workers face the highest inflation levels in 40 years, after it hit 9% at the end of May.
On Tuesday morning, stations which are usually filled with commuters were left almost entirely empty except for picket lines by union members.
Figures published by location technology firm TomTom show the level of road congestion at 8am was higher than the same time last week in several cities.
In London, congestion levels increased from 77% on June 14 to 98% today.
Other locations with worse traffic included Hull (from 55% to 59%), Liverpool (from 48% to 55%) and Newcastle (from 50% to 57%).
The figures represent the proportion of additional time required for journeys compared with free-flow conditions.
Watch: Train stations deserted as Britons hit by major travel disruption due to rail strikes
There were also severe queues on outer London sections of the M1, M4, A4 and A40.
People trying to travel around the capital faced long queues for buses.
Uber hiked its prices amid a spike in demand, with a three-mile journey from Paddington to King’s Cross estimated to cost £27 at 8.45am.
Much of Britain will have no passenger trains for the entire day, including most of Scotland and Wales, the whole of Cornwall and Dorset, and places such as Chester, Hull, Lincoln and Worcester.
Last-ditch talks failed to resolve the bitter dispute over pay, jobs and conditions, with all sides blaming each other for the lack of progress.
Around 50,000 members of the RMT union at Network Rail and 13 train operators have walked out.
Strikes are also planned for Thursday and Saturday.
London Underground services are also suspended on the vast majority of lines today due to a walk out by workers.
Prime minister Boris Johnson is expected to say ahead of a Cabinet meeting that unions are “harming the very people they claim to be helping”.
He is set to accuse unions of “driving away commuters who ultimately support the jobs of rail workers”, while also hitting businesses across the country.
He will say: “Too-high demands on pay will also make it incredibly difficult to bring to an end the current challenges facing families around the world with rising costs of living.
“Now is the time to come to a sensible compromise for the good of the British people and the rail workforce.”
RMT general secretary Mick Lynch said Network Rail had offered a 2% pay rise with the possibility of a further 1% later dependent on efficiency savings.
He told BBC’s Newsnight that Network Rail had “escalated” the dispute during Monday’s talks, saying: “They have issued me a letter saying that there are going to be redundancies starting from 1 July.
“So, rather than trying to come to an agreement in this dispute, they’ve escalated it by giving us formal notice of redundancy amongst our Network Rail members.”
He warned that the dispute could continue for months, adding: “It is clear that the Tory Government, after slashing £4 billion of funding from National Rail and Transport for London, has now actively prevented a settlement to this dispute.”
The Department for Transport disputed Mr Lynch’s clams, adding that it has cost taxpayers about £600 per household to keep the railway running during the coronavirus pandemic.