The cost includes the fee for the vehicle, excess waiver insurance (EWI), SatNav, an extra driver and 40 litres of unleaded fuel. With weekly costs of £547, Croatia worked out as the second most expensive destination for British holidaymakers to rent a car. France came third with total fees of £447.
In comparison, the Danish capital of Copenhagen is the least expensive for the same seven-day package and at £248 is less than half the Portuguese price. The second cheapest in the table was Germany with £264 and the Netherlands was the third cheapest at £277.
The Post Office says the strengthening pound is encouraging Britons abroad to splash out on car hire.
The Post Office was quoted as saying that at least 20 per cent of UK holidaymakers stated they would be hiring vehicles for their European holidays this summer. It noted that not only was the fee for the vehicle itself cheaper, but fuel to fill it up with was too.
Ireland's car rental costs are in the middle bracket at €551.The Excess Waiver insurance was €128 and payable excess €1,346.
Sources: Post Office, The Irish Times, Carrentals