Possible to resit GCSE maths in one year?

Very possible, for gcse maths get a past paper and do it, identify errors and use the textbook or examsolutions, as for the a levels if you have your notes and the textbooks just skim read/review them and practise past papers. Then attempt other exam board past papers.

Just stay consistent if your busy on day x find 20-30mins of your time recapping topics.

Definitely. While you may be doing other resits too, as long as you put enough time aside to just read over the maths topics, attempt questions and do past papers properly you should be fine.

What I'd do is get yourself a textbook or two such as the CGQ books which are quite handy for GCSE maths, and just do a topic every other day, read through them and attempt any of the example questions and just practise until you're good with the topic.
After you've had a chance to grasp most types of maths questions judt start doing past papers, mark them and keep a record of your scores and go over where you're going wrong.

Video tutorials may help quite a bit too, I used ExamSolutions for A Levels as he gives tutorials on each topic and does video solutions for past papers, believe he does just as much for GCSE level too.

So there ya go, short answer is yes it is definitely possible, just make sure you know when your exams are and how to structure your revision ahead of time.

Thanks very much for the help, also i guess i have all the motivation in the world knowing if i don't then i can't get into Leicester uni! and thanks i'll look into all the resources you've posted. Is there also somewhere i can find just a simple list of every possible topic in the edexcel because i find the textbooks have a lot of unnecessary stuff, so i just needed a checklist to ensure i cover everything. Also, is there anything you recommend for the longer questions? these are what really confuse me as i'm generally fine with math and doing calculations but sometimes i don't know what calculations i'm meant to be doing :/
Cheers!

As far as a check list, maybe the specification on the exam board's website would be useful? However when it comes Maths I tend to not use the spec as much and so don't really know what they're like to use as a guide.
My recommendation would be, if you don't necessarily stick to the textbook (still recommend using one but if you feel there's stuff there you don't need perhaps don't focus on it so much?) then speak to a GCSE maths teacher who teaches for the exam board you're doing and ask them for a list of all the topics/sub topics. Otherwise ExamSolutions has a list of pretty much everything with links to guides so check it out

When it comes to getting your head around specific questions such as those involving more reading, the best way to get good is just practise so you can identify common phrases and such between different questions as these will usually guide you to what you're supposed to be calculating. Sometimes information is given in the question which yiu may not realise is that important but it could be you need it for a calculation later, and so they key is to identify anything important in the question as that can indicate what you may be looking for later. Sorry this is vague advice but without specific examples I can't really tell you what to look for and it's been a few years since I touched GCSE questions, if you have any you want to send me then go for it. Like I said, practise, practise and practise :' The more you deal with the type of questions you're gonna get in the exam the more familiar it will feek when you actually do them.

Thanks so much for the help, just had a quick look at exam solutions and its like a spec anyway and are you at uni now? If you weren't to busy it would be helpful if you have whatsapp and i can ask you if i need help, but if you're at uni dw as you'll be very busy haha!

As far as I'm aware they have a new grading system for GCSE's this year (I may be wrong). This is based on a 1-9 point system, where 9 is the highest. There is no longer an A* grade, but an equivalent grade which is either 7,8,9 (I'm guessing). Also there are now 3 papers marked 80,80,80 I believe. I apologise if I completely wrong, hopefully someone clarifies.