Ammon News - The prices of flights and hotels for new green list travel destinations have swung sharply in both directions since the guidance was changed on Thursday.
The government added 16 destinations to the list. Travellers returning from these do not have to isolate on return.
Destinations include Malta and Spain's Balearic Islands, and some holidays have doubled in price, the Independent's travel editor Simon Calder said, as reported by the BBC.
Airlines have added extra capacity.
Initially when these new flights have become available, prices have fallen as extra supply takes up the demand.
But this has proved to be short-lived in many cases: "Availability is changing by the minute," said Mr Calder, who has been checking prices regularly since the announcement, according to the BBC.
"Immediately after it was made there was still quite a lot of keenly priced flights and holidays, but we're back down to 'last seat' showing."
"Madeira and Malta, for example, were looking pretty reasonable, but then things really took off. Unless you're sitting in front of a screen there's no way of gauging which trend line you're on," he added.
EasyJet said: "When new flights are put on sale the starting fares may be lower compared to existing flights with many seats already booked.
"Like all airlines, our pricing is dynamic which means that our fares start low and increase the closer it is to the date of departure and as more seats on the aircraft are booked."
The destinations added to the green list from 04:00 BST on 30 June are:
Europe: The Balearic Islands (which include Ibiza, Menorca, Majorca and Formentera), Malta and Madeira
Caribbean: Anguilla, Antigua and Barbuda, Barbados, British Virgin Islands, Cayman Islands, Dominica, Grenada, Montserrat and Turks and Caicos Islands
Other British Overseas Territories: Bermuda, British Antarctic Territory, British Indian Ocean Territory and Pitcairn
Six destinations will also be added to the government's red list on 30 June. They are the Dominican Republic, Eritrea, Haiti, Mongolia, Tunisia and Uganda.
Operators contacted by the BBC were concentrating mainly on satisfying demand for the Balearic Islands, Majorca, Menorca and Ibiza, and Malta.
BA said it was reviewing its schedule and had added some additional flights and upgraded some routes to larger aircraft, for example to Malta and the Balearic Islands.
EasyJet said it was also adding seats and holiday packages and new routes, also focussing on Malta and the Balearics.
New routes to Malta from Bristol and Luton will launch next month and offer some seats at £27.99.
Ryanair said it was selling 200,000 extra seats on flights from the UK to Malta, Ibiza and Palma for July, August and September.
Ryanair's Dara Brady called the latest announcement a "small step in the right direction" but called on the government to add Cyprus, the Canary Islands and Greek islands to the green list.
Jet2holidays said there had been a "huge surge" in bookings.
It reported the highest volume of bookings to the Balearic Islands in almost a year, with bookings for July alone up more than 3,000%.
Bookings for Malta and Madeira also jumped by almost 1,500%.