Job offer withdrawn

I was wondering if anyone could help me,

I recently applied for a job in the civil service, I passed the exam, and then got an interview.

I'm currently in my final year in college and won't be finished until may, I made this clear in the interview and was told it would not be a problem.

I then received a letter confirming that I had been successful in my interview and was offered a job.

The next day I received a phone call from the department offering me the job, I accepted it, then when I told them when I could start they told me I would be unable to start at that time in that department, that they would send my form back to the office and I would be reassigned to a different department.

I wrote to the office to tell them about this, and the man in charge rang me back and told me that If I can't start before the 19th february then I wont be given a job. He said that there are jobs available for may but if I want to start then I have to reapply and go through the whole process again.
I informed him that I was told in my interview that I could start in may, he said that they thought it would be ok then, but now its not.

Is he allowed to do this?

I don't think that there is anything to stop an employer doing this. In fact even if you do take up a job you have no security of tenure until after 12 months service.

I read this on an english website, I'd say the rules would be fairly similar here

As soon as you have been offered a job, and have accepted it, this forms a basic legal contract between you and your new employer, even if you haven't yet received anything in writing.
If that offer is subsequently withdrawn, your employer has 'breached' the contract. It may be possible for you to sue your employer as a result, particularly if you have suffered loss because you have left your previous job to take up the new offer.

I don't know whether it would apply to me or not though.

My point is that the contract in question is largely useless since they could hire you for a day and then tell you that you are no longer needed. You could hire a solicitor and try to pursue this through legal channels but (a) it may not do your job prospects much good with the same organisation and (b) you could well end up losing more than you stand to gain.

I dont want to sue or anything, I just want the job, I'd understand if the job wasnt available or anything but the jobs sitting there, and I passed the exam and interview, theres no reason why they shouldnt give it to me.
They just said that when they began the competition they thought it would run until may, but now its only running until february, and although there are loads of jobs left, technically i have to apply to the new competition starting in february.