Go to their flagship store in Primrose Hill(they have 3 branches-Kensington and Covent Garden) and have a chat with a manager.
You'll then be offered to do an unpaid trial for 5 hours where you get no break and virtually no training as such, left to your devices with another colleague while the manager goes away to kitchen at busiest time.
Then if successful you'd be called for further trials consisting 10.5 hours which is paid at minimum wage.
If you are then successful, they will need 2 satisfactory references from your former employers.
In a nutshell, so much hardwork and exploitation just to get a job at a coffee shop that only pay a measely 7.50 per hour.