Hello and thanks for using Just Answer.
I am Al and am happy to assist you with your enquiry.
Well, by far the quikest, cheapest and most effective thing to do is to write to the Mortgage Company, confirming that there are these arrears. A Mortgage Lender will always pay any arrears directly, as they can then re-coup it from the borrower under the Mortgage conditions.
I am not sure if the property is still in the joint names of both parties, but if it is in the sole name of the lady, then she, as Leaseholder, is responsible for the payments as opposed to the man, who is the Director.
A Notice confirming who the Mortgage is with, should have been served on the Freehold Company by the parties Solicitor when they purchased the property, so you should have their details. If not, you can go on the Land Registry website and obtain a copy of their Deeds for a nominal fee, (called "Official Copies") and the Charges Register will confirm the name and address of the Mortgage Company.
A short letter to the Mortgage Company is all it will take for the payment to be made, and hopefully will mean that you won't have this continual problem in the future.
I hope this helps you and answers your question.