Holiday companies have laid on extra flights to the Iberian nation to cater for the bounce in demand.
However, the country’s government has extended its “state of emergency” until at least 30 May, which could scupper holiday plans.
According to the UK’s Foreign Office, travel to Portugal for Britons is restricted for essential purposes only, which does not include a holiday.
The country has yet to officially decide whether Britons will be allowed in, and what the requirements will be if they are.
Typically, PCR tests need to be taken within 72 hours of arrival, which would require travellers to organise them over the weekend for a Monday trip.
It’s understood a decision will be taken today about whether to grant entry to Britons.
This morning, Portuguese MP Cristovao Norte told BBC Breakfast that a decision should be taken “immediately” on whether British tourists can enter Portugal from 17 May.
Mr Norte, who is MP for the Algarve, said he did not know whether Britons will be allowed to visit the country from Monday.
“We are today going to make an urgent inquiry asking the (Portuguese) government whether or not the English travel can come to Portugal next Monday because we are three days ahead from 17th and no one is sure what is going to happen,” he said.
Mr Norte added: “Our vaccination process is going steadily and it is important a decision is taken immediately.
“The message is clear, there are no reasons, nor political or scientific reasons to maintain restrictions for travel from the UK to Portugal.”
Asked if the decision could change between now and Monday, he said: “It's possible but I'm not sure what's going to happen.
“Yesterday there was a council of ministers and the minister responsible told the press they didn't have a definitive decision.”
According to the BBC, Portuguese Cabinet office minister Mariana Vieira da Silva said in a briefing yesterday she had “no information to give yet”.
“Work is going on and as soon as there is a decision it will be announced, but no decision was taken in this cabinet meeting,” she said.
The decision will also affect thousands of football fans. The Champions League final has been rescheduled for Porto on 29 May, a decision which has seen air fares to the city spike.
Additional reporting by agencies