Workers across Britain have lost out on holiday pay worth £2bn, with more than a million people going without a single day of paid time off, according to new research.

With unions gathering in Brighton this weekend for the first TUC conference under a Labour administration for 15 years, the body revealed new research showing the extent to which workers are being denied holiday pay. Workers are entitled to 28 days paid leave for a typical five-day week.

The research, conducted before the government’s pledge for a generational improvement in workers’ rights, found that 1.1 million employees – about one in 25 – did not get a single one of those days. It said that black and minority ethnic staff were disproportionately hit. Low-paid workers were most at risk of losing out on paid holiday. The roles with the highest numbers of staff losing out were waiters and waitresses, care workers and home carers and catering assistants.

It said that holiday pay was just one of a number of basic rights that many workers were missing out on, blaming a lack of enforcement on issues such as the minimum wage and the legal right to a wage slip. The TUC called on Labour to move ahead with its promised Fair Work Agency, a new overarching watchdog with the power to prosecute and fine companies that breach the rights of their employees.

Paul Nowak, the TUC’s general secretary, said the new watchdog must have “real teeth” to succeed. “More than a million working people have been deprived of any of the paid leave they are due, and hundreds of thousands more have been denied basic rights like being paid the minimum wage,” he said. “Now it’s time to reset the dial and to end the Tories’ race to the bottom.

“These shocking findings show why we need the employment rights bill and the Fair Work Agency. Working people deserve to be treated fairly and have a minimum floor of rights upheld. There is huge support from the public – right across the political spectrum – for this.”

The research comes with the Labour government and the trade union movement largely aligned heading into the TUC conference. In the run-up to the election, most Labour-affiliated unions remained extremely loyal to Keir Starmer, with Unite emerging as the only large union to raise serious concerns about alleged backsliding on Labour’s programme to improve workers’ rights.

Since the election, the chancellor, Rachel Reeves, has pushed ahead with pay deals for NHS workers, teachers, the armed forces, train drivers and junior doctors, seeing the agreements as a crucial early step to boost the economy and attack some of the barriers to growth. The party has already in effect abolished a Conservative law forcing certain sectors to ensure a minimum level of service during industrial action.

It has become a point of attack for the Tories, with Conservative leadership candidates accusing Reeves of making deals with unions while removing winter fuel payments from the vast majority of pensioners. Reeves has said there will be no “blank cheques” for unions, despite the flurry of settlements since the election.

However, difficult political issues for Labour will still be raised and debated at this weekend’s conference, including calls for a wealth tax on the richest 1% and further public ownership for industries such as water and social care, as well as the renegotiation of the Brexit deal with the EU.

The forthcoming employment rights bill, expected to be introduced by the government next month, will ban “exploitative” zero-hours contracts, end the “fire and rehire” practice, and make parental leave, sick pay and protection from unfair dismissal available from the first day of a job. Union officials are watching closely for any signs that the measures are being diluted or delayed, but most remain supportive of the programme.