Kate Simon: Before you think of putting those keys in the ignition, read this

The nation may still be picking Christmas tree needles out of the carpet, but the February half-term holidays are drawing near. So, it is a timely moment to consider some of the problems you might face if you're heading off on a break that involves hiring a car.

Take the recent experience of Annie Noble, a reader from Dorset, who has alerted me to the questionable practice of a car-hire firm that she used in Spain. On arriving at the Goldcar desk in Girona airport, she was asked to pay £60 for a full tank of petrol – the company's policy is to fill the tank and ask that the car be returned empty.

Annie, like most of us, had ignored the small print on her car-hire voucher, but her points are valid. What happens to the fuel you don't use? The next hirer must surely pay for it a second time. And how can this be good practice environmentally? It encourages drivers to maximise their mileage to make sure every drop of fuel is used up.

Goldcar was unavailable to answer these questions. But a spokesman for Auto Europe, through which Annie hired the car over the internet, confirmed that it does use local agencies that operate this policy. He said the company requires ground agents to refund the cost of fuel left if the rental is for three days or less, but not if the rental is for four days or more, because it believes the petrol will be used up in that time period. Unfortunately, not in Annie's case ...

Travellers may find hire cars are as rare as hens' teeth this summer, according to Economy Car Hire. It blames the recession, which it says has resulted in a lack of investment in fleets and a decline in car production. It warns that a repeat of last summer's crisis, when prices doubled, is on the cards. Economy was selling a week's hire of a Ford Ka in August for €117 during January 2009, but the price soared to €240 for anyone booking in the month of August itself.

The company predicts summer shortages at destinations including Portugal, Spain, Italy, Croatia, Greece and Cyprus. It says pre-payment is essential, too, because anecdotal evidence shows pre-booked cars sometimes "did not materialise" on the ground last year.

Is this a ruse to get us all booking early? Not according to Carrentals.co.uk, which confirms the experience of lack of availability of cars for hire. "Spain was particularly badly hit last summer," a spokeswoman said. You have been warned.

The latest edition of Which? Holiday says new research shows some hire contracts have "potentially unfair terms", such as stating that if customers could not produce the keys in the event of a car being stolen they would be liable for the full value. Hard luck if the keys were stolen at the same time, or if you have been the victim of a car-jack.

Which? Holiday says it studied the online booking process for eight of the main car hire companies for London's Heathrow airport and Charles de Gaulle airport in Paris. It found Avis and Enterprise had no information about terms and conditions of hire on their websites, so customers couldn't read contractual information before booking online. Alamo, Budget and National provided some but not all of this information on their websites.

It seems that even if you do always try to look at the small print, sometimes it's not there to read.

Do you have a travel issue to raise? Email sunday travel@ independent.co.uk