Mind I don't suppose Ive got anything to lose by giving it a whirl?
Well, only your confidence, etc., perhaps.
The exam must cost the same if you book through an instructor or direct by myself.
It would but you will have to know when and where and how to and the ABRSM can be a bit snotty about who enters you, etc., and - as I say - a teacher will know all the little tricks about when and where to take an exam. For example, you can take your exam at an approved ABRSM teacher's home. This is a much more relaxed and comfortable experience, usually on better pianos. And different home venues are better than others. Alternatively, the exam could take place in the upstairs of a local music shop or at a school on a piano that's been banged about by loads of people. A teacher will know all the local ins and outs. You will not (and I doubt very much you as a private individual could manage to secure an exam at an approved home).
If I fail ill still be drastically further ahead than I am now.
You might not. You might have just spent/wasted a good few months teaching yourself bad technique playing pieces that are irrelevant to you. Even with a teacher, the pieces may be irrelevant but they (and the scales, arpeggios, etc.) are structured to build your technique gradually over the grades which can then be applied to playing stuff that IS relevant to you. A teacher will (or should) also spot your weaknesses and structure your practice regime to overcome those. You won't on your own - you'll just keep banging away thinking you're making progress but more than likely reinforcing bad technique and not overcoming weaknesses.
You COULD do it yourself in theory but it's going to be a tall order and I fear that disappointment lies ahead for you. Sorry but there is no easy (or necessarily cheap) way round this - if you want to learn to play properly, acquire good technique and go through the grades (or even get Grades 1 and 2), you will need a (preferably good) teacher.
Looking at the other thread you have started about scales, you're tripping up over your first scales - not a good sign. Rather than engaging in pages (and days) of (possibly futile) forum discussion (and still ending up none the wiser or more confused than when you started), a teacher could help you with that in a matter of moments simply by showing you!
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