Well, firstly deeds have long since been done away with and it is what is on the Register at the Land Registry that counts now. One way to check this is to click
http://www.landregisteronline.gov.uk/ and follow the instructions (you only need look at the Register). Secondly, what used to be called a charge is now called a restriction but the effect is the same, it stops the property from being sold until, in your case, the debt to the bank has been paid. So, if the restriction is on the Register your mother (if she is now the owner of the property) cannot sell until arrangements to pay off the bank are made, and if it is not on the Register nothing is owed and all is clear.