I feel I ought to belatedly explain the two year approach.
You are a credible Oxbridge candidate, at least 2A*s in your predictions, probably more.
You want to go to a top five University. (I may arouse more controversy here, but feedback is that people with say A* in further maths who opt for course content rather than the course reputation, can find themselves understretched.)
Top five Universities in popular subjects can be very oversubscribed. They are often the courses that appeal to strong international or European students, plus University fees seem to have encouraged students towards quasi-vocational degrees (engineering, economics, law, medicine, computer science, maths and science).
Competition then can be tough, and it is perfectly possible, even with a 4A* prediction, to be rejected not just by Oxbridge, but by places like Warwick and UCL. (I know because it happened to DS!)
If you get the grades in the summer, there is a decision to be made. Either you take the course you firmed, or if it does not really appeal, you apply again, this time with achieved results, a stronger PS buoyed by things you did over the summer, and and a year's extra maturity which should help your interview technique.
Universities have to treat all home/EU candidates equally so I assume if you have a stronger application, you stand a better chance. (Maths may be different in that not doing maths for a year might make you a weaker candidate - I don't know.)
The thing to watch for is rejecting a good second choice in order to have a second go at Oxbridge. Anecdotally, and based on very small samples, the Durhams, LSEs etc can read this as not being that interested in their course. It is not unknown for very confident candidates to only try for Oxbridge in the first cycle, leaving other choices to be fall backs for a second attempt.
Leave the decision till results day, and then, if the results are really good, have a hard think about the extent to which you might regret not having a second attempt at Oxbridge. In short how much better FOR YOU is the Oxbridge course compared with the one you have firmed.
Gap years and a second application can be good things in themselves. DD has been surprised at how often adults have shared their fond memories of ski seasons and Camp America, and so far she is having a great time whilst looking forward to a summer in upstate New York, whilst picking up a range of softer skills which will be useful in any future career. With every chance she will appreciate University more when she finally get there.
Whilst we do know several kids who have got Oxbridge on reapplication, we also know one prospective student, A* in everything, applying for a very popular course, who got feedback along the lines of that he had been an excellent candidate, but so too were the other eleven they had interviewed, and they could only take four. He revisited his firm after his results and decided he wanted to try Oxbridge again. He did not get in, but by the time he came to decide which offer to accept, his priorities and interests had changed and he is now very happy in London (which he had not applied to first time round) and on a slightly different course. Plus had a great year off.