Is it true that long-term use of Tenormin causes Diabetes Mellitus?

A patient is thyro-toxic and hypertensive and taking Tenormin(Atenolol) since a long time. It is said that long-term use of Beta-Blockers like Atenolol may cause Diabetes Mellitus. To how much extent it is true or not?Is it true that long-term use of Tenormin causes Diabetes Mellitus?
That would be very difficult to answer accurately as the main cause of high blood pressure is the same as the main cause of type two diabetes.... Poor diet/lack of exercise. So, how can you separate the lifestyle effects from the drug effects?Is it true that long-term use of Tenormin causes Diabetes Mellitus?
In randomised controlled trials beta-blockers have been associated with a doubling of risk of diabetes compared to other antihypertensive medication.