Thanks for that information. The taxi was only 12 eruos so it wouldn't have been worth risking a 40 euro fine (albeit a very small risk). In fact, I didn't realise that the hotel I'm staying at is so quick via taxi so I'll probably use this mode of tranport for getting from the hotel to the airport from now on (we're talking 10 minutes in a taxi instead of over half an hour on the public transport).