This question crops up a lot on this site. Most people merely copy the question and sit there, open-mouthed, waiting for the answer to drop in. You've had the decency to be honest about what you are doing.
I would look at the latest Barclay's Annual Report to shareholders and any other useful looking press releases. See here: -
http://www.investorrelations.barclays.co.uk/BR C1/jsp/brccontrol?task=articleFWgroup&site=inv &value=1169&menu=395
As to today's key issues, I don't hold the monopoly on the truth, but perhaps start with something around how the global banking community should rebuild trust in the wake of the US sub-prime fiasco. If that sounds a bit heavy, you could also try something around how UK banks can keep costs down and still offer adequate levels of customer service - stuff around the value of offshore Call Centres.
As an HR professional, I suspect its not about getting what Barclays think the right answer is, its about coming up with something tangible that you can defend your corner at interview. HTH