Both good replies above. You are not legally able to touch your mother's bank accounts unless you apply for Lasting Power of Attorney and then, as has been said, the money can only be used for your mother's benefit and evidence must be kept on this.
However, it's a much more strict process now. Enduring power of Attorney, since 2007 ,has been replaced by Lasting Power of Attorney and you need one person for welfare matters and another for finance and property. You can't in fact do anything until this has been set up and processed.
People with existing Enduring Power of Attorney before 2007 go through an easier route as outlined by Naomi in the posting above this.
This website will give you more information, but I would also contact a solicitor to guide you through the process.
I have been through all this recently and it's not easy. I too wish you and your family luck.