life insurance covers you if you die, life assurance covers you when you die, income protection (IPI) covers you if you are unable to work due to sickness, mortgage protection covers you if you are unable to work through accident, sickness or unemployment for no more than 2 years. IPI is very important as it is designed to kick in when your employer starts paying you SSP (c£10/day). My wife, self employed, is currently being paid 65% of her gross income as she is off work following bereavement reaction - neither ASU and life cover would obviously have been of any use in this situation.
Contact an IFA to discuss, don't try to work it out yourself as unless you do it every day you're likely to come unstuck.
Brian