Chris

AFAIK you have very few rights one way or the other, certainly with regards to to dismissal. However offering you a fixed contract has additional benefits to the employer such as the ability to exclude you from any benefits you might otherwise be entitled to (e.g. staff discount, if one is applicable to that business). I worked for a company for 18 months recently, on three consecutive fixed contracts, which excluded me from the pension scheme and bonus scheme amongst other things - and the automatic end-of-year pay rise. I had to renegotiate my salary at the end of the second contract.

It may also be useful to your would-be line manager; if the company is trying to keep head-count down, fixed-term employees can be hidden as project costs rather than normal HR costs.