Foreign Secretary Dominic Raab said the Government would "not apologise" for reimposing strict quarantine rules at short notice on travellers returning from Spain.
Ministers announced on Saturday that holidaymakers who had not returned from Spain and its islands by midnight would be forced to quarantine for 14 days after Covid-19 second wave fears saw the European country struck off the UK's safe list.
The sudden timing of the announcement was criticised by the travel sector and consumer rights groups but Mr Raab said the Government had been right to take "swift" action.
The decision was made after Spain recorded more than 900 fresh daily Covid-19 cases for two days running.
Mr Raab told Sky News' Sophy Ridge On Sunday programme: "The data we got was on the Friday, it showed a big jump right across mainland Spain, that was then assessed yesterday afternoon and we took the decision as swiftly as we could.
"And we can't make apologies for doing so.
"We must be able to take swift, decisive action, particularly in relation to localised, or internationally in relation to Spain or a particular country, where we see we must take action.
"Otherwise, we risk reinfection into the UK, potentially a second wave here and then another lockdown.
"So, yes, I understand it is disruptive for those going through this who are in Spain or have been considering going but we must though be able to take swift, decisive action to protect the UK because we've made such progress in getting the virus down and prevent the virus retaking hold in the UK."
The Cabinet minister conceded there was an "element of personal responsibility" involved when telling those returning from Spain to self-isolate but stressed there were "penalties for non-compliance".
Labour criticised the Government's handling of the decision, labelling it "frankly shambolic".