I'm thinking of buying a remapped ecu just wandering if it is plug and play or if there is anything I would need to do, cheers.

I'd suggest you leave the ECU where it is.

 

When you get a remap done a skilled mapper would do a dyno test before he started remapping to get a baseline reading. This would allow him to customize the map to allow for the current condition of the engine, turbo, injectors etc based on the initial reading. 

 

How much is the ECU? It may be coded to the car it came off so unless you get it coded to your car it would be an unattractive paperweight. There are people who remove the immobilizer chip from VAG ECU's making the car potentially easier to steal.

I believe it is from pd parts and around £70 

 

Looks like a good deal, I'm guessing that price is exchange without surcharge.