Rubbish agent - what to do?

[YukoandHiro]

I'm trying to sell my flat in London. Had four valuations, came in at two different price points between them. I went with one of those who had a higher estimate, nor because we were being greedy but because they had what seemed to be a much more effective marketing strategy.
Three weeks in we've had no viewings. Four were booked and all cancelled by the clients (suspicious?) And the market is moving extremely fast. We've already seen and lost two properties we really wanted to move to and could afford, but couldn't offer on because we're not proceedable til under offer.
We're trapped in for the contract now (12 weeks I think) and prices are bound to dip in June. I just feel so frustrated.
Has anyone managed to kick a shit agent into action, and what did you say/do?

Yes, when selling my parents house.

After three months with little interest, I went multi-agency. i.e. appointed a second agent, but on a fixed price, no sale, no fee basis. I did pay the Rightmove and Photography costs for the second agent up front, assuming that two agents would mean two exposures on Rightmove etc and I wanted good photos for both.

I then requested the Righmove figures re ad viewings, click through etc. from both agents on a weekly basis. I also asked for info on number of people already on their books who had been contacted, telephone contacts, number of brochures sent out etc.

Interestingly the initial agent really upped his game when I did that and sold the property within a very short time.

He tried to charge me a multi-agent rate for that sale, but I was able to argue how appalling his performance had been until the second agent was appointed and we reached a fair agreement on his revised fees.