The number of people who work night shifts has increased to more than 3.1 million after a big rise in recent years, a study shows.
The TUC said an extra 275,000 people worked nights between 2011 and 2016, taking the total to one in eight of the UK's workforce.
Women account for more than two thirds of the growth, following an increase in care work and nursing. Men are more likely to have night jobs in security, police and transport.
The biggest increase in recent years has been in London, followed by the South West and Wales, said the TUC, adding that the trend is likely to continue because of the Night Tube in London and proposals for a seven-day NHS.
TUC general secretary Frances O'Grady said: "Tonight most of us can look forward to an extra hour in bed, but as we sleep, millions of workers will be busy keeping the UK ticking over.
"Whether it's nurses looking after patients, or police officers keeping our streets safe, we all depend on Britain's army of night-workers.
"Night work is hard and can disrupt family life. So we must show our appreciation for the sacrifices night-workers make by ensuring they have good rights and protections at work.
"Employers must play fair and play safe, or public safety will be put at risk and the families of night workers will suffer."