renault 04 plate key that needs to be coded for the vehicle

You can not. That is part of the security system.and it makes some extra money for the producer.

You can not re-code the key.
The key has a permanent code - it is the car that is programmed to recognise the key.

After some thefts last year, Renault has instructed its dealers not to reprogramme cars unless they also supply the key (the dealers need to get a code direct from Renault to perform the reprogramming). Proof of ownership is required before they will supply a new key, or reprogramme the car.
Contact your local Renault dealer.