This is one of the simplest, most practical Brompton accessories.
It's a cloth basket, with a removable metal frame. It features an open top for easy access to your belongings, and drainage holes in case of rain. It has a 24-liter capacity, and folds neatly out of the way when it is not in use.
If your Brompton does not already have a block for front carriers installed, you will need to order one.