As discussed in the article on registered keeper v/s legal owner
, only the legal owner is entitled to any rights on the car. So if your mother is the legal owner and you are having financial problems with the bank, then the bank in question cannot legally seize and dispose of the car because you do not have any rights on the car itself.
As an example, there are many people who drive company cars (as travelling may be a major part of the role) and are therefore listed as the registered keeper in the logbook. However they cannot sell the company car because they have no rights on it. And if they were to find themselves in financial hardship, then debts collectors would not be able to sell the company car to get their money back because the car does not belong to the driver in the first place.
Unless the bank has towed your car away, you shouldn't worry about getting a solicitor.