UKGrad - the Big 4 (and similar) firms got really burnt in the post dotcom downturn, they'd not taken their foot off the gas in terms of hiring and so had to make a lot of people redundant. Their employer images were tarnished for several years thereafter.
As a consequence, they've been very quick to react to changes in the economic climate ever since. The financial crisis in 2008 was swiftly followed by a curtailing of graduate hiring - and a programme of delaying the start dates of those grads they had already made offers to.
The period since then has really been characterised by the firms turning the hiring taps back on and off again as a function of the prevailing market sentiment. Given the uncertainty arising from recent developments in the Eurozone, I wouldn't be at all surprised if firms are reappraising their willingness to commit to graduate hires and are stalling on making hiring commitments and / or reassessing the start dates they can commit to.
On a positive note, I therefore would say this behaviour is likely to be entirely a function of market uncertainty - and caution on the part of the firm - rather than any cooling off in terms of their interest in you personally. I'm not in frequent contact with the consultancies regarding their grad hiring as we focus mostly on experienced hires, so this is just my informed opinion. If I were in your shoes, I think I'd be inclined to approach the firm and address the elephant in the room. Say you can understand their caution in issuing offers for the current year and could you propose proceeding with a contract for a delayed start date a year later. I suspect there'd be a decent chance of this being accepted and you could then join the firm / practice you've set your sights on - and concentrate on finding something fun to do with the intervening year.
Hope this is helpful.
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