CPT, which represents the bus and coach sector, said passenger levels were at about 40% just before Easter.

But companies are expecting more people to be travelling as lockdown measures ease further from 12 April, with shops and outdoor hospitality reopening.

In Wales services are at 80% of normal levels, while in Scotland they are at 95%, according to CPT.

From Monday in England, non-essential shops and close-contact services like hairdressers and beauty salons can reopen, while pubs and restaurants can serve customers outdoors, as part of the next stage of the roadmap out of lockdown.

In Wales, non-essential shops and close-contact services can also reopen from Monday, while in Northern Ireland the stay-at-home message is being relaxed and non-essential retail can operate click-and-collect.

But in Scotland people will have to wait until at least 26 April for more of the economy to reopen.

Bus services fell to around 80% of pre-pandemic levels in England during the third lockdown that began in January, compared to around 50% during the first lockdown in March last year, according to CPT.

However, they increased to 100% as measures were eased over the summer.

A spokesman for CPT said: "Operators have reacted flexibly during the pandemic to respond to passenger demand and with the reopening of non-essential retail and outdoor hospitality now is the right time to increase service levels to help people visit shops and see family and friends.

"The industry will be closely monitoring passenger demand as restrictions ease to ensure that services are at a level that allows passengers to travel safely."

Welcoming the return to normal services, chief executive of the Bus Users charity Claire Walters said: "Buses are the most used form of public transport and are vital to the UK's recovery.

"Millions rely on them to access work, education, training, health services, leisure facilities and shops, so the sooner we can get people back on board, the better for everyone."