I dealt with many letting agencies in London and the KFH in Wimbledon has the worse staff ever, if you go there don't ever ask for Tammy.
They rented me a house where I did not have hot water for 10 days. There was no way to contact the landlord and no way to even hear back from the agent. From the beginning, the agent was not replying to any of my emails or returning any of my calls regarding some very important issues I had with the apartment.
They lied about my electricity bills as well. When I received the bills I was shocked, the power supplier's estimated prices were 3 times higher than what the agency had told me! I cannot afford that and would never have moved to this flat if they had told me the truth about the electricity bills! This is not even over yet, and I am willing to take some legal action against them.
Clearly, tenants are just a tool to look good in front of landlords, they have made it very clear that their customers are landlords and not the tenants. In 1 year we dealt with 3 different people regarding a bad condensation in the flat, and that means explaining the situation 3 times. Very rude customer services, ignoring any phone call we ever had, and blame it on us and dare to ask for more money... Basically, the worst year I've ever had in my life is with them. Good luck!