A few options were suggested:

• London School of Photography offers a 5-day Photojournalism & Street Photography course in London, which is likely the closest match to an intensive documentary-style class.
• Another route is to look through local photography press/classifieds, where short discipline-specific workshops are often advertised.
• You could also consider self-paced training (for example through organizations like the Open University) or brand-sponsored workshops, though these may be less documentary-focused.
• If you’re open to traveling beyond the UK, a Mary Ellen Mark workshop was mentioned as a strong documentary-oriented option.

For documentary photography specifically, the most useful searches will usually be around terms like photojournalism, documentary photography workshops, and street photography courses, since providers may use those labels interchangeably. Before booking, check whether the course includes field shooting, editing/review sessions, and portfolio feedback, since those are especially valuable in a short intensive format.