What happens to a UK commercial mortage when the account holder dies?

My father died in November and held a mortgage with Commercial First on a business property. The business closed on his death. I'm currently waiting for a Grant of Probate to enable me to deal with my father's estate and Commercial First won't discuss the mortgage with me until I have this (expect to receive this in 5 weeks). They are currently adding a �130 arrears charge to the account each month in addition to the monthly payment and threatening to begin reposession proceedings. What I want to find out is, once we have the Grant of Probate, are we able to pay off the mortgage in a lump sum from my father's estate without having any early repayment charges? Will the additional payments and arrears charges in the 4 months since my father's death need to be paid or just the amount that was owed on the date of his death? Can they repossess the building before we have the Grant of Probate? My father didn't leave a will so we have no authority to deal with his estate until we have this. As this is a commercial mortgage, it is not regulated by the Financial Services Authority. Any help would be much appreciated! Thank you in advance.