There's no way the other party can dispute liability if their vehicle caused damage to yours. The important thing is that they're insured, as it's under that contract of insurance that you're covered under the Road Traffic Act. Ask your insurer to contact the at fault party's insurer, advising that they require to inspect the other party's vehicle to carry out a causation report. They can then establish whether that vehicle has been involved in a collision with your vehicle. It is possible another vehicle has been on fake plates and hit your vehicle, and the other person is telling the truth, but should they have damage to their vehicle this will quickly unfold. You can then leave it with your insurers. Alternatively, issue proceedings directly against the driver of the other vehicle and put them in a position where they will be in contempt of court for lying under oath. This is a much more severe situation to be in than they may have envisaged.