References which pass from one employer to another are covered by what is known as qualified privilege. This means that an employer can probably say what s/he likes about an employee. However s/he must not:-
give any information about convictions that have been spent
maliciously make false statements
negligently make a wrong statement. The House of Lords has decided that an employer giving a reference about an employee owes her/him a duty of care. This means the employer could be sued for negligence if the reference/testimonial contains inaccuracies which result in the employee suffering a loss.
You really need to see the reference and decide whether it contains untrue/defamatory statements.