So, after seeing this TerraClean process done to a Jag on Wheeler Dealers, I decided to have it done on my own car. It's meant to remove built up carbon deposits and clean the internals of the engine, as well as the injectors. So I went on their website and found my local garage that does this, and booked it in. £80 to have it done and it takes 2 hours.
First of all, the fuel lines are disconnected and then plugged into this magic machine


The engine speed is set to ~1800rpm, and left for 20 minutes

The engine is then switched off, and the product left to "soak" for a further 20 minutes

The engine is then run for 20 more minutes to blast out the deposits. After the process was done, I was amazed by how much quieter the car is. The turbo spools up sooner and there is no more hesitance. Hopefully I should see some fuel economy improvements too!

Just for the record, I'm in no way affiliated with this company, just sharing a good experience.

Benjamin