I have following offers:
MSc management course from WBS, MSc business analysis and Strategic management from AMBS, MBA from Strathclyde and Birmingham.
I have 4 years of experience working as a Risk advisory consultant in a Big 4 audit firm in Asia.At the time of leaving, I was working as a senior consultant. My experience is in performing Internal audits, process improvement assignments, control gap assessments and development of SOPs for different business processes. In future,I wish to continue working in the field of consultancy.
After graduating, I am targeting a role of atleast senior consultant/associate in UK firms.
I have budget constraint and cant afford MBA from a top university.
I have a BSc degree in accounting and finance and want to diverse to gain broad management knowledge which may be better suited and add value to my profile considering my experience in advisory consultancy.
So my question is what would u recommend, MSc from a top business school or doing MBA from a mid tier university? And what should be my preferred course choice from the above mentioned?
Will be really thankful if u could share your useful insight!

Are you looking to broaden into another type of consulting or stay within advisory?

As you are already at a Big 4 firm, is there an option for you to stay with the same firm and transfer to their UK practice? If so, have they indicated whether that pathway would be dependent on getting a Masters degree or is there another possible development route?

Yes, i am looking to broaden my role in consulting also. Currently, it is mostly focused in accounting and finance related areas.
Further, it is not possible to transfer to Big 4 firms in UK and there is no such pathway for the same. My reason for pursuing Master's qualification, specially from a reputable university,  is because it's still preferred by Big 4 firms in term of promotions and career progression.

Have you considered delaying a year and then, with 5+ years of work experience, applying to higher-tier MBA programs?

Your Big 4 experience will be valuable but really, the best advice, in terms of career progression, seniority level, and salary, is to aim for one of the ranked MBA programs, the higher the better. 

I am aware of the fact that higher-tier MBA programs are far more preferable in terms of career progression, but i don't think i will be able to afford it even next year. Its way to expensive from top business school ranging from 40,000 pounds to 50,000+. 

I am targeting a role of at least senior consultant/associate in UK firms which i think i can achieve even with a Master's qualification from a reputable business school. I can consider doing an MBA later if i feel the need for it.  
So from the above options, which one would u say should be my preferred choice. 

PS:What i have heard from the university alumni's, WBS program is general and more theortical and class avg age is 22. Whereas AMBS program is a bit more practical with students coming in with some prior experience.

Are there people with your background who get hired as senior consultants in the firms you are targeting with just an MSc? Most MBAs will be hired as associates. 

I think you might be assuming a lot and could benefit from more research. Many FT ranked MBAs and MSc cost under £40,000. The UK is not the only country, but it does have the most expensive higher education in the EMEA region.