The cheapest time to travel to Portugal and Spain typically falls in the shoulder seasons, specifically from late autumn (October to November) and early spring (March to April). During these months, airfare and hotel rates drop due to fewer tourists, but weather remains pleasant for sightseeing.
The most affordable travel times to the UK are generally in the winter months (January to February) excluding Christmas and New Year holidays, when travel demand is low and prices for flights and accommodations decrease.
To maximize savings, plan trips to Portugal and Spain during March or November, and the UK in January or February. Booking flights at least 2-3 months in advance further reduces costs.