Tell them your situation

Tell them your situation, tell them how you feel bad about it. Tell them your family situation. Tell them you really did not took so much. But most important you should collect proof that you did not take that amount.Tell your duty counsel your possible plan and ask for his suggestion.

The bill and book together still can not prove you take so much (The owner may will take that to show how much you take), since other people can take either and also mistakes. Video tape can just prove you did take some money in most case but not amount. Show your bank account, show you expense, get some witness to prove how poor you are (That is not shame being poor).

We are human, not God. We, for some reason and sometime, make mistake. Theft in that amount (1000 pound)is not a big deal.

Now you can not leave UK without explain since they possibly can put it into media, that will be worst situation.

Now, collect evidence to prove you did not take that much, do some calculation and give it to your free lawyer. Do not controle your emotion when you explain to judge and lawyer.