Plant at least three detectives in Vauxhall? (10)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

[ PI(abbrev. for “private investigator”/detective) + DIS(abbrev. for more than 1 “Detective Inspector”) ](making 3 or more detectives) contained in ( in ) ASTRA(a model of car manufactured by Vauxhall Motors Limited).