What man of 30 wants to go out with a 17 year old? At 30 he has been working for years and probably went to university. Woman of his age want adult relationships and after a period of time may want to get married, have kids or buy a house.
Woman of around his age have life experience and can spot the red flags of an immature man who refuses to grow up. They can also spot the men that are mean or expect things there own way always.
My feeling is that he is with your daughter because he wants sex and wants someone who thinks he is great. She probably thinks he is great because he has a car and money when the lads of her age are lucky to have minimum wage job on a Saturday if they are still in school.
He is grooming her and why have you not told your husband about this relationship?
You need to tell your husband about him and decided then how your going to get him away from her. I wonder would his boss like to hear how he using his job and possible position of power to go out with staff years younger than him?
He may have form for doing this.
I hate to see your daughter decide that she not going to college after her A levels or going to a local college to stay near him. I also hate to see her getting pregnant. He won't want her or a baby if this happens. Then you don't want to be dealing with her pregnant and trying to sort out an abortion for her. Then if she keeps a baby it will have a major impact on her life and yours also.
You want your daughter to stay in school, get her final school exams, go to university and get a decent job. I know girls that are now in their early 20's and they are either finishing university or in there 1st graduate job's. They are in house shares, going out with friends and going on cheap holidays. They are going out with lads around there own age and enjoying life.