Summary dismissal is usually a result of gross misconduct. An employer has a duty of care to other employees, so it's likely that he did something inappropriate with incontrovertible evidence (most likely text messages). As a result, an ad hoc investigation was conducted, and HR advised dismissing him with immediate effect.
But also, this could have been kept under wraps while a proper investigation was carried out, leading to his dismissal. Such matters must be kept confidential until a decision is made anyway. Either way, he’s been a wee creep.
Though I’d go with summary dismissal since his lawyers are looking at it. Wouldn’t be surprised if he’s back on BBC, since it’s the BBC we’re talking about, and all feckery they’ve let go on over the years.