England I need to get hold of a fully working DOS computer, with a working CD Rom, hopefully a working 3.5" floppy.?

look on ebay and sort by 'distance', you'll probably find an old desktop or laptop with a working Floppy drive.

go with a laptop rather than a desktop, you probably wont find any MS-Dos computers with a CD rom drive, those didn't come into use untill much later, dont even think they are compatable with the old MS dos computers.

and a laptop because you wont find the keyboard or mouse to go with a desktop, they dont use the same connectors as now and compatible keyboards/mouse are hard to find.

if your just looking for a system to run old software/games on, you dont really need a whole computer, you can run it on any computer using Dosbox.

http://www.dosbox.com/download.php?main=1

and maybe buy a USB floppy drive.