Really bad quality disposable camera?

It's not necessarily bad quality, as much as disposable cameras lack control over the exposure which leads to inconsistency, so in difficult conditions you may only get 1/4 useable shots. Then consider the space that such a camera would take up, at 27 frames a camera, you'll probably need 15 cameras for each week you are there. It's far more sensible to take a inexpensive film camera, and some film. It will be both cheaper, and more relible, you'll probably only need half the amount of film too. You could buy a Olympus Trip 35 (which has a 40mm f2.8 lens), for around £10. An Olympus OM20 with a 50mm f1.8 lens is around £30-40. My Olympus OM-2SP only cost me £15, which is a bargain, and my OM 50mm f1.4 was only fiver, though I had to repair it myself.

Argos Disposable Camera

Go for the camera with the highest ISO film inside, probably 800 ISO. Sit it somewhere hot (really hot, parcel shelf of car in direct sunshine) for a few days before or after taking the photos. That will probably mess up the pics sufficiently. When you get the film processed (developed) ask for a CD to be written also - it will only cost a pound or two extra. If the pics don't look messy enough you can always add more grain and mush in Photoshop or other software. Actually, if you have a digicam, just mess those digital pics up in the computer.

Grain in film is caused by the ISO of the film - it has nothing to do with the camera. The higher the ISO (it's sensitivity to light) the more grainy it will appear.

If you want bad quality photos try the lomography technique of just taking bad photos ;) or try dropping the camera a couple of times to hopefully introduce light leaks (where the camera back lets light in).

When you take your photos to be developed, ask them to put them on a CD for you. Most places in the UK will do this for a little extra charge (or it may be a standard part of the service).

alternatively, you will need to either scan the negatives in a scanner that can scan film, or scan the prints.

You could of course avoid all that trouble with just mangling your pics in the image editor of your choice - either way the images are almost guaranteed to come out bad.

you could always get some disposable cameras and "destress" them to come up in a bad way... like light leaks...