It also found packages offer "much greater protection if a trip is affected by coronavirus or other disruption".
Which?, which released the results in a press release, looked at the price of the cheapest package holidays available online from five UK airports from both Jet2holidays and Tui, and compared them with the cost of identical DIY holidays.
It found the package holidays were cheaper in eight out of 10 cases – with the biggest saving of more than £400 on a holiday to Greece.
In the examples Which? looked at, researchers calculated the cost of the DIY package using the cheapest airfare from the same airport on the same date as the tour operator package, and included one check-in bag per passenger. The cost of return airport transfers was also included in the DIY bookings if these were included in the corresponding package booking, to create an identical holiday.
The biggest saving was £442, for a two-week holiday for a couple flying to Rhodes from Bristol, booked through Tui. The same holiday with travel and accommodation booked separately would cost £1,025, compared with £583 when booked as a package – an increase of 76%.
The average saving across the eight packages that were cheaper than a DIY booking was £157.
Only two package holidays worked out more expensive than their DIY counterparts – one Jet2holidays trip to Salou and one Tui holiday to Majorca. But even when it was cheaper to book flights and hotels independently, the maximum saving was only £31 per person.
Almost all tour operators do not operate packages to countries where the Foreign Office (FCDO) advises against non-essential travel. They will cancel the holiday and refund customers if that advice changes at short notice due to coronavirus or another reason.
"On the other hand, throughout the pandemic many airlines and OTAs have continued to fly to countries where the FCDO is advising against non-essential travel due to Covid-19 and have refused to refund passengers who follow the guidance and do not travel," Which? said.
Rory Boland, editor of Which? Travel, said: "Throughout the pandemic, we’ve been urging holidaymakers to book a package if they were considering a holiday over the summer or are looking to book for next year, given the unparalleled protections they offer if things don’t go to plan.
"Many people are put off booking a package because they worry they’ll have to pay more than booking their flight and accommodation separately, but as our research shows, a package could save holidaymakers hundreds on the cost of their holiday.
"Not all holiday providers are equal, though. Anyone planning on booking a holiday for 2021 should strongly consider booking a package with a reputable provider that has treated customers fairly in recent months, to ensure their cash is protected if something goes wrong."
