You could be charged, under Section 5(2) of the Criminal Law Act 1967, with 'wasting police time'. The maximum penalty is 6 months imprisonment and/or a fine of up to �2,500.
Both your question, and my answer, use the word 'could', rather than 'would'. A prosecution for wasting police time can only be brought by, or with the consent of, the Director of Public Prosecutions. No such prosecution would be brought until the circumstances had been thoroughly investigated.
Example 1: A woman complains that her husband has beaten her up. She gives a detailed statement to the police. They take photographs of her injuries and get a doctor's report regarding the likely cause of such injuries.
The woman later seeks to withdraw her statement. In such circumstances, no action would normally follow against the woman. However, the police and the Crown Prosecution Service would still seek to convict her husband, using the other evidence which they have.
Example 2: A woman accuses her ex-boyfriend of raping her, out of shear malice. She later withdraws her statement. Obviously, the Crown Prosecution Service will not continue with the case against her ex-boyfriend. The police would then compile a file on the case and send it to the Director of Public Prosecutions. The DPP would have to decide whether it was in the public interest to charge the woman with wasting police time. (It's quite likely that a charge would follow but there might be special circumstances, such as the woman's mental health, which would make the DPP decide otherwise).
Chris