Theft can mean such a wide range of things and for this reason its understandable that the sentencing guidelines for simple theft is very wide.
Punishment for theft can start as low as a discharge or band C fine all the way through Band B fines, and community orders.
As the details of an offence become more serious then custody options all the way up to 7 years are available to the court.
The sentence would depend upon the circumstances of the case.