I actually spotted this Gro Anywhere Blackout Blind on Mothercare for £30, but decided to price compare and see if anywhere had a better price. You can buy this item for only £23.95 including free delivery from Amazon. It's also £30 at John Lewis, £31 @ Kiddicare, etc.
I think this is an excellent idea and it will be going on my wishlist for when the baby comes!
From a quick glance at the product description, it's a heavy duty blackout blind, which fits on any window via the use of little suction cups. It means that if you are travelling anywhere, even visiting family for the day, you can pack the blackout blind with you. Then the baby can comfortably nap anywhere.
* Lightweight, light-proof material; Designed with travel & versatility in mind
* Adjusts to fit nooks & crannies of any shaped window
* Eyelets at regular intervals on the hem mean you can pop in suckers only where needed depending on the window
* Each hem can also be shortened for a proper fit
* Easy to use - put up & take down takes just minutes; Packs into a handy travel bag; Generous size - 200 x 135cms