You can get special dimmers that link to each other and they decide which is in control depending on which one was operated, but I haven't seen them in this country, they were made by Switchlinc. I used a couple of them when I was stateside and they seemed ok. I think Smart Switch made em as well for here, and sold them through B&Q, but it was years ago I looked for them. The biggest problem with them was that they required a neutral as well as the switch wires, so if your house is wired using loop-in neutral you're goosed unless you bring a neutral down from the light to each dimmer.
For normal run of the mill dimmers, only 1 is fitted, the other end must be a standard two way switch.