Someone who failed their dissertation for bad plagiarism in my MA year, got London Met to let her in to just redo her dissertation there. I thought that was very bad standards on their part at the time, but she failed again apparently. I now wonder whether it was a cynical money-making attempt on their part, so you might want to be very careful about any offers that look too good to be true. I think the OU only let you transfer a lower number of credits than you have towards a qualification there, so you would need to repeat more than the dissertation. I would expect the same to be true of most places.