Divided by a Common Language in The London Eye

While reading Siobhan Dowd's The London Eye Mystery as a judge for the Cybils middle-grade fiction category, I came across a British term I didn't know. Since I like keeping up with British terms, this both intrigued and annoyed me.

Here's a passage with the word in question. Can you spot it?

Salim slept on the lilo next to my bed that night. I'd hardly ever had to share before. My hand shook itself out. Salim shuffled into a sleeping bag without saying much.

A quick Google search showed me that the word "lilo" has several common meanings--common as far as the internet is concerned:

• Software for loading Linux.
• Title character in one of Disney's last successful traditionally-animated movies.
• Gossip-column abbreviation for Lindsay Lohan.

And Wikipedia listed several other possibilities.

None of those was right, obviously. In The London Eye Mystery, the lilo is what teenagers have to sleep on while Aunt Gloria gets a real bed. So it's either a mattress or a cot--but which?

It turns out "lilo" is a British term for what we Americans call an "air mattress." Furthermore, the Brits use the same word to refer to a pool float while we Americans seem to keep those flat inflatable objects in separate mental categories.

So now I'm wondering when the term "lilo" became established--perhaps from the brand name Li-lo. And are there class or regional overtones to its usage that I'm still unaware of?