im looking for some advice please guys.
my coop has recently been written off by the insurance company.
i have seen a turbo plus for sale for £3ooo
its done 128,000 miles
has full service history.
is it worth it given the milage ?

Read the buyers guide to start with, then go see the car. milage is not a major issue as long as its been loved.

Better to go for Markus' car for 3.5k in for sale section IMO

There's nowhere near enough information in that post for anyone to make any sort of judgement on the value of the car. Rather than mileage, you need to know what works be done on it, what major jobs have been undertaken, the car history (hpi check), what garage has been doing the work etc etc...