Bamber was very unsure about whether he called Julie before or after the police. Eventually settling for after. Although two witnesses say the call to Julie was at least 20 minutes earlier. Even under cross examination.
Saying he called Julie after the police means that he couldn't say he called her for advice. He had already made a decision to call Chelmsford and agreed to meet them at WHF.
It is not logical to call Julie after Neville had called him and he had called the police. He didn't have time and hearing 'a friendly voice' is not required or beneficial. It was also 3am and Julie may not be a 'friendly voice'.