Travellers arriving in England, Wales and Scotland from Thailand will no longer have to quarantine from this Saturday.
Along with Singapore, the popular holiday destination has now been added to England and Scotland's travel corridor following a drop in coronavirus cases.
Similarly those arriving in Wales from Thailand will no longer have to quarantine, along with Gibraltar returnees.
However, for all three nations, anyone arriving from Slovenia and Guadeloupe will now need to self-isolate for 14 days following a significant increase in confirmed Covid-19 cases.
The new quarantine measures come into force from 4am on Saturday, September 19.
Data from the Joint Biosecurity Centre and Public Health England has indicated a significant change in both the level and pace of confirmed cases of coronavirus in both Slovenia and Guadeloupe , leading to Ministers removing these from the current list of Travel Corridors.
It showed there had been an increase per 100,000 cases from 14.4 on September 9 to 29.1 on September 16 in Slovenia - a rise of more than 100%.
Announcing the latest changes to the travel corridors list, Transport Secretary Grant Shapps tweeted: "Latest data shows we need to remove Slovenia and Guadeloupe from the Travel Corridor list to keep everyone safe.
"This means if you arrive in the UK from these destinations after 4am Saturday, you will need to self-isolate for 14 days.
"Separately, we will be adding Singapore and Thailand to the Travel Corridor list. Please check before you travel as both countries may have extra requirements before entering.
"A reminder that travellers to the UK (from ANY location) MUST complete a Passenger Locator Form by law. This is vital in protecting public health & ensuring those who need to are complying with self-isolation rules."
Scotland's Justice Secretary Humza Yousaf said: "Managing the risk of importing cases from communities with high risks of transmission is vital in our efforts to suppress the spread of the virus in Scotland and imposing quarantine restrictions on those arriving in the UK is our first defence.
"We continue to closely monitor the situation in all parts of the world and base the decisions we make on the scientific evidence available.
"We are also in regular discussions with the other three governments in the UK.