An interesting sounding event, London Craft Beer Festival is a flat rate entry event, that gets you 5 hours of entry, a glass, a programme and a third from every brewer there (at least 18, the website has some conflicting information). Not certain how it works, but I reckon CBR style tokens will probably be involved.
Tickets are required (these cost £35), and can be bought here (scroll down to August to find the slots). There are 3 days to choose from. (16th, 17th or 18th August), but the Saturday afternoon slot seems a reasonable choice.