In the UK a contractor could be someone from an outsourcing company as you suggest or they could be an independent service provider working on their own. This is very common in software dev here when you require someone with specific skills.

If you’re the latter kind then you’d be wise to bill on deliverables rather than time.

If you don’t you could run into a well known tax reg called HMRC IR35. It bars independent contractors from acting like “disguised” employees. It’s a world of pain if that happens.