i can't give back Student Grant.. which consecuences?

Hello,
I would be very grateful if you could help me giving information about the following problem.
I've been living in london for about 5 years.
During the last year 2007/2008 I decided to start university, and i decided to ask for student support.
The support was divided into a maintenance grant (non refundable), a maintenance loan (refundable) and a tuition loan (refundable).
I left london suddently in march/april due to a severe personal problem.
I didn't take much care to inform SLC that i was leaving school and the UK,
Then, few month ago i discovered that a debt collection agency was looking for me at the old address in london,
and a friend opened my letters lying there. Student Loans Company and enfield council sent letters saying that because i stopped my university course before the end, the last installment of maintenance grant was not really due, and i would have to give it back immediately.
I don't have that money anymore, and due to my personal problem i am still not working, so, can't give anything back yet.
Now i must go in london a couple of days to pick-up my cats (i left them at my neighbours house, but now they can't host the cats anymore so i must go up and take arrangements for them..)

My question is: knowing that a debt-collection agency is looking for me in england, what should i expect going back there?
can the police arrest me for debts?
can they hold me in england against my will?

If you need any other information or detail, please ask me.

Thank you very much for any help
Andre'