I think it sounds like a good idea to help out your daughter, and if you are never likely to fall out it could work. However, do be careful of other, third parties. I put my name to the mortgage on my daughter's house, so that it was in our joint names as they would not have lent her the money on just her salary. Then the boyfriend moved in. After seven years, although the house was in her sole name by then, he managed to claim half the equity simply for living there. They had split up and he refused to move out until she had remortgaged and paid him off.

If your daughter gets a flatmate, be sure that it is a legal agreement that the flatmate is a tenant, and nothing more. I would strongly advise you to seek the advice of a solicitor before going ahead.

She should also have life insurance to cover your contribution. It is not something that you want to think about, but what will be your position if anything happens to her? I would also make sure that the flat is in your names as joint tenants.