Many of the cheap Spanish car hire firms offer a “full to empty” policy – you pay for the full tank (at an inflated price) when you pick up the car and can return it empty. It sounds convenient but adds extra cost, particularly if you are not going to drive far and won’t use the full tank you paid for. But as drivers have steered away from the full to empty deals, some rental firms block a significant amount on your credit card to cover the cost of the petrol, then charge an administration fee even if you return with the tank full, typically €25-€40.

6. Avoid adding a second driver unless it’s free

Having one driver reduces costs by a huge amount. Typically, car hire firms will charge about €6 a day for additional drivers but have a minimum fee of €18. At Centauro in Spain, the cost for a “basic” car at €7.74 a day quadrupled to €27.81 a day with the “premium” package that includes an additional driver.

7. Book a four-door car

If the price difference between a two-door and four-door vehicle is negligible, always book the four-door. Car hire companies frequently run out of four-door vehicles in their cheapest “mini” or “economy” categories, so if you insist on them giving you a four-door vehicle as booked, they have to move you into a better category car without being able to charge you.

8. Take your own child seats

Even though Ryanair charges £15-£25 per flight for carrying child seats, it can be cheaper than renting on arrival. Car hire operators will charge as much as €95 for a child seat on a two-week rental. You also can’t be sure of the quality and fit, so it’s better to take your own.