Selling jointly owned home?

My girlfriend wants to sell her house which is jointly owned with her ex boyfriend. Her ex boyfriend is continuing to live there and has agreed to the sale of the house with a local estate agents, but the property is not selling. The house is currently marketed at a much lower price than it is actually worth since it is subject to a local occupancy clause. I feel the estate agent is not marketing the property very well - they only use internet and the house is in a rural area so not many people will pass by and see a For Sale sign. I have suggested that another estate agent markets the property, but, her boyfriend refuses - he is obviously very happy to keep living in a house with his new girlfriend whilst my girlfriend must continue to pay half the mortgage.

What can we do to try to get this house sold? Could we force sale via an "action of division and sale" through the courts? If this is possible can someone please explain how this works? Are there any other suggestions?

All serious help is gratefully received.

Thanks