One of the big trends in the hotel world at the moment is pop-ups; some hotels have pop-up shops, others have pop-up bars or restaurants; and there are even pop-up hotels.
It's not just hotels; there are pop-up cinemas, like Films at the Yard which popped up in the East End earlier this year and pop-up shops all over the place. There's even an entire pop-up shopping mall, the Boxpark in Bishopsgate, based in shipping containers.
London hotels are trying to outdo each other with original ideas for hotel pop-ups - like this vintage shopping boudoir at Andaz Liverpool Street
The advantage of a pop-up rather than a regular outlet is that you can be much more adventurous, since the pop-up only has to cover its costs for a limited period, not for a whole year. Christmas pop-ups were much in evidence at the end of 2011, with Niko B's Santa Baby chocolate shop popping up at Avo Hotel in Dalston, and chocolatier William Curley running a pop-up shop in St Martin's Lane. There was also a party to promote the pop-up Pudding Parlour in December at the Athenaeum that our bloggers reviewed.
Meanwhile, Bourjois decided to set up a pop-up shop in Shoreditch just for London Fashion Week and Andaz London had a Vintage Shopping Boudoir hosted by fashion blogger GIRL.STOLE.VINTAGE. And there's an ongoing Luna & Curious shop at The Sanderson.
Pop-up pudding parlour at The Athenaeum
Last summer, the Langham had a pop-up Terrace Bar offering Pimms and champagnes, as well as sushi or meze sharing platters; The Goring went even further with a pop-up Caribbean beach bar.
Garden spaces are likely to host more pop-ups this year – with the Montague on the Gardens fastest off the mark already with its fabulous Secret Garden (the same hotel also did a pop-up ski lodge over the winter!).
Pimms station with smiling staff in the pop-up "secret garden" at the Montague on the Gardens Hotel near the British Museum - part of a trend of hotel pop-ups
Pop-ups also allow a hotel to host celebrated chefs or designers and gain kudos by doing so. For instance, this summer the Sheraton Park Tower will host a pop-up of Bukhara, the iconic Indian restaurant in the Maurya Hotel (New Delhi). While Claridge's is arguably trumping the lot with a pop-up version of award-winning Copenhagen-based Noma to coincide with the London Olympics – with head chef René Redzepi personally in residence.
There are even pop-up hotels – though quite often, the snazzy term is merely borrowed for something that's basically just a short-term rental.
One recent experiment was the Hotel Alcatraz, near King's Cross, which saw guests incarcerated for the night, relieved of their possessions and made to knit to ‘earn' their stay – an interesting concept but not really much competition for London's mainstream hotels.
Hotel Alcatraz was an example of hotel that is itself a pop-up 
Still, I was intrigued to find out that a real pop-up hotel company came to the stock market recently. Snoozebox makes portable hotel rooms, for use at music festivals and other big events; like Boxpark, it uses old shipping containers as its raw material.
It's apparently going to help house 600 performers at the Diamond Jubilee pageant at Windsor Castle, and has also housed attendants at Go-Kart championships. According to estimates it could be worth around £20m – that's quite a lot of hotel!
Photo credits: Andaz Liverpool Street, London Hotels Insight blogger Timea, www.Laterooms.com (Hotel Alcatraz photo).http://londonhotelsinsight.com