Uni offers, conditional/unconditional. Is it first come first serve?

3 years I attended an open day at Durham. The lecturer there said they had over 1000 applications and only offered 400 posts. They new from experience that this would give them the required amount of entrants I believe it was 180. If there was more than that then that was their problem as once they made an offer they could not withdraw it. This was also said by Bath. Durham then explained the applicants fell into 3 groups. Some were rejected and others were accepted early. The third group was left until after the January deadline before making a decision as they had to give equal consideration to those making applications up to the deadline.
As far as unconditional offers are concerned many unis failed to recruit enough students last year. Partly because some unis like Exeter and Bristol had increased their intake and also the amount passing at aab and above fell. Unis are now offering unconditional offers to ensure their intake doesn't fall this year.
With your predicted grades I don't think you will get a problem unless it is a select course at a select uni.

I think you are mistaking what I am trying to say here. Durham was used as an example to show how unis keep places open until the deadline and how unis stick by the offers made. As I said you are not likely to have any problem unless you later decided to apply to the likes of Imperial LSE Durham and maybe a couple of other unis for specific subjects such as Warwick for Maths Kings for Law etc as the students applying there are likely to have as good or better grades than yours but for the vast majority of courses and the unis you are applying for there should not be a problem