They all have strong reputations for getting their MBA graduates into consultancy.
You could look on their websites or email to ask them if they publish the exact proportions of graduates entering the sector.
Perhaps the more useful differentiation for you will come when if you look at the three school from the perspective of which sector and function focus you will want to adopt in your consulting career.
For example, Cranfield has a good reputation for transitioning engineers into other career paths. Warwick has a reputation for bringing in strong operations management/O.R. and finance lecturers. Manchester has a good reputation for international business/economics, org. behaviour, and marketing.