Most people have by now become aware of the requirements regarding passport validity and length of stay:
Your passport has to be valid for 3 months or more after the day you leave Mallorca. In addition, it has to be less than 10 years old when you travel to Mallorca.
While UK nationals don’t require a visa when visiting Mallorca as a tourist, you can only stay for a maximum of 90 days in any 180-day period.
Anyone visiting Mallorca from a third country. Tourists need to:
be in possession of a return or onward ticket
have proof of address for the duration of their stay
have sufficient funds to support themselves during their holiday (€ 100 per day).
While this last requirement is the one that seems to have caused the biggest outcry, it does make sense, considering the fact that third-country nationals are not allowed to work in Mallorca or Spain without a valid visa issued for this purpose.