I think the concept of a farm in central London in great, and I know there are a few around. On one of my usual Thames walks this weekends, I came across this little farm - a farm next to the Thames was even more of a novel idea.
The farm is quite small but has a number of animals. Unless you're really into the urban farms, I wouldn't make a special trip, however I would plan it into a day if I was in the area. What was great, was a room on the farm you could rent for parties - so a great place for children's birthday etc.
Entry is free but donations are suggested at £3, this inner city farm is a charity and can only survive from donations so please make them!
Cost: £3 donation suggestion
Location: Surrey Quays