According to my mechanic it will cost €600 to have the chain and tensioner's replaced. Seemingly buy from Peugeot as its a Peug engine and the parts are a lot cheaper
The PSA (Peugeot) engine wasn't put in Mini's until the Mk2 came out in 2007. Prior to this the engines were a Tritec Rover/BMW joint developed unit. The OP's car is a 2003.