No, far more appropriate is page 116 (Witness Intimidation). This is a more serious offence than the Harassment without Violence offence on page 70 and can be charged whether violence is threatened or not.
You will see that the “starting point” for this offence is custody and it carries a five year maximum sentence when dealt with at the Crown Court. It can be used to prosecute before a case is concluded and up to 12 months after the matter has been finalised.