I worked in consulting side at a Big 4 firm before bschool, so perhaps I can chime in. (I worked in US, not in UK)
It's common practice to force one to start all over again when switching from one Big 4 to another Big 4.
1) Each Big 4 firm thinks they are better than the other
2) Unless you were working in exactly same line of business, you have to start over again because you can't manage bunch of other consultants if you don't know how to do their job to begin with (at least that's what Big 4 believes)
Since you worked at your respective firm for only about a year, starting over is not that BIG of a deal. Usually in the consulting side, you can move up rather quickly if you can do your job well, AND show some potential that you can bring in new clients (or work with others when courting/proposing new business proposals to potential clients).
Deloitte is trying to compete with McKinsey in the management consulting business (although I have my reservations about whether this is possible or not). They are trying to merge with a german consulting firm, but that other firm rejected the proposal.
If you feel that compared to what you are doing now at your firm, the line of work in Deloitte Strategy is sort of an upgrade, you should consider switching. You only have one yr of experience and compared to people with multiple years under their belt, it is rather easier choice to switch if you feel that Deloitte work is an "upgrade" compared to what you are doing right now.
Prestige? Compared to other advisory services that Big 4 firms offer, strategy consulting should expose you to interesting work. Some of Deloitte's clients for strategy consulting isn't too bad, especially in Europe. I've met some ex-KPMG and Deloitte consultants from UK currently matriculating at Columbia Business School over the summer in NY - so I guess for bschool purposes, it isn't too bad either.
Again, make the switch if you feel that you are going to like that line of work. Don't accept a job offer for prestige or bschool purposes. More often than not, it will backfire on you.
GMAT Club Premium Membership - big benefits and savings