Iv recently bought a skoda octavia vrs tdi, the cars done 138k and is puffing out blue smoke on start up and the turbo is making a police siren noise on boost, I'm pretty sure I need a new turbo but is there a possibility it's the valve stem seals? Any advice would be great! Thanks.

Don't know about the siren noise / turbo, but with the oil, how much is it losing?

Not much, hasn't moved in a week but it does come out a fair bit! I have been told that it's the turbo oil seals going, allowing oil to escape and get into the exhaust system..

Police siren noise is certainly sign of a turbo failure, yes.