Deregister for TRS query - Ulster Bank Mortgage

Hi,

I'm currently filling out form TRS4 to deregister for TRS. It requires that I input my Loan A/C Number - on my Ulster Bank Home Loan Account Statement, there are two numbers quoted (Mortgage No and Account No - both have same no of digits)

Could someone tell me which one I need to input? Sorry if it's a stupid question, but I want to get it right (and can't get through to Ulster Bank this morning!).

Thanks,
Maggs

Account number.

Thanks Joe