When she last went to pay her ground rent of £1.50 my mother was told there was no need to bother any more, because the freeholders were no longer interested in receiving the money. Is this the end of the matter, or should she be seeking some sort of written assurance regarding the lease?
Your mother should try to get something in writing, and I recommend that she continues to observe the terms of the lease. It would be very nice if the freeholders were prepared to transfer the freehold into your mother’s name, and it might even add to the value of the house. However it might cost money: how much would depend on whether the freeholders decided on a valuation to determine the market rate, although it’s possible that she could apply to purchase the freehold at preferential rates anyway.