i went thru this process recently. firstly you will need to contact your mortgage company and they will tell you what they require from you. they will more than likely tell you that you need a solicitor as there is legal work involved. i initially rang round some local firms and was getting quotes of £500 upwards. i finally settled with doing it with an online solicitor which cost a total of £240 -much cheaper and very easy.i had to fill out a detailed application form with the mortgage company with job history, incomings and outgoings,etc and proof of income -ie recent wageslips and proof of any benefits as the loan is changing from the responsibilty of 2 people to 1 they want assurance that you will be able to meet the payments.(it is almost like you are applying for a mortgage from afresh) i don't think the amount outstanding will alter how the mortgage company deal with this.are you and your ex partner agreed on how the equity of the property is being split between you as this is obviously a big factor if you have paid a lot of the mortage off.