Year out before Masters? UK

I'm currently a final-year student at a semi-target university in the UK. Recruitment hasn't gone my way this year, and it's been tough securing interviews. My career aspiration is to work in investment banking. I can attach my CV for you to review. Currently, I'm "working" part time at a two-man boutique firm ran by an ex-Goldman employee. Deals are slow-moving, and I don't get paid, but I do get to work on some aspects of the process (presentations/paper work). 

I'm questioning the current issues/worries preventing me from applying to a master's program right away:  

1. My grades are poor right now. I currently have a 2.2 but hope to graduate with a low to mid 2.1. So I don't have much faith in getting into Oxford/LBS with my grades right now.

2. The market is currently awful, and it's more competitive than ever. I heard most of the top master programs took a hit to IB recruitment. 

3. I'm currently considering applying for a deferred MBA but would appreciate more time to study for the GRE (I believe master's students can apply for a deferred MBA).  

If I were to take a year out, it would take the pressure off and allow me to focus on my university work and apply for off-cycles. Regarding any "gap" on my CV, I could fill it in by stating that I was working at this boutique firm for most of the time. 

With a year on my hand I can study my GRE, prep for technicals, and hopefully end up at a top master program during a decent market environment for IB recruitment. 

I think this would give me the best chance at succeeding as it'll allow me to hit the ground running and be more prepared.