>>>I suppose it depends on what sort of convictions he has had
No it doesn't.
Unless the type of employment is exempted from the provisions of the Act (as would be the case when working with children or vulnerable adults, or within the administration of justice), once a conviction has become spent that's an end of it. It doesn't matter whether the conviction was for violent assault, theft, sexual assault, or anything else. If it's spent it doesn't have to be declared.
Conversely, where the type of employment is exempted from the provisions of the Act, all convictions have to be declared, irrespective of their nature. (So, for example, a 55yo teacher who was convicted of not having a TV licence when he was a student 35 years earlier must still declare that fact when applying for another teaching post).
Since nothing in Broseph's post suggests that his friend's employment application is for a job within an 'exempted' sector, he definitely does NOT have to declare his spent convictions.