Look up per diem reimbursement rates and mileage deductions for business travel worldwide.

Complete
United Kingdom → Porto, Portugal
Item Name Destination Amount Conditions
Meals Oporto, Portugal 35.5 EUR per day Over 5 hours rate: covers subsistence expenses for a period of more than 5 but less than 10 hours, measured by reference to the times of arrival in and departure from the foreign country.
Meals Oporto, Portugal 88 EUR per day Over 10 hours rate: covers subsistence expenses for a period of more than 10 but less than 24 hours, measured by reference to the times of arrival in and departure from the foreign country.
Meals and incidentals Oporto, Portugal 93 EUR per day 24 hour rate: covers the total cost of meals and daily hotel-to-office travel for a full 24-hour period.; The actual room rate is paid in addition to this amount (source shows the rate as 'plus room rate').
Lodging Oporto, Portugal 130 EUR per night No specific conditions
Breakfast Oporto, Portugal 0 EUR per meal This amount is included in the room rate, so it is not paid separately on top of the lodging rate.
Lunch Oporto, Portugal 32.5 EUR per meal No specific conditions
Dinner Oporto, Portugal 49.5 EUR per meal No specific conditions
Incidentals Oporto, Portugal 0 EUR per day Source row labelled 'Other': other expenses incurred during the day; employers may use the individual meal and other rates instead of the over 5 hour, over 10 hour and 24 hour rates.
Drinks Oporto, Portugal 6 EUR per day No specific conditions
Transport Oporto, Portugal 5 EUR per day Covers daily travel between the employee's hotel and office.
Total residual Oporto, Portugal 93 EUR per day Total residual rate: intended to cover the total cost of meals in a period of 24 hours plus the cost of daily travel between the employee’s hotel and office; the 24 hour rate is the sum of the room rate and this total residual rate.

Source URL:
https://www.gov.uk/guidance/expenses-rates-for-employees-travelling-outside-the-uk
This source provides official travel rate information from gov.uk.