if a person has hypertension and a little bit of back ache which is controlled by medicines and is well under control, can do utthanapadasana or not?or do you suggest raising single leg instead of both legs.please advise
In terms of hypertension this is a safe asana and if your HBP is under control I cannot see the danger in it. In terms of a bad back, it might pose certain challenges and you should perhaps exercise more care in pointing the toes when you lift and pushing out in the heels when you lower the legs down to the ground, this will protect the lower back.
However, we don’t know how bad is your back and I understand from your post that you take medicine for it, so please be careful as the medicine might mask the pain and you might think everything is ok and in the mean time it is not. 
I’d like to turn the question around.
What is the need or purpose or intention for the specific asana you are asking about?