Download and print a lost or theft of passport notification LS01 form (see resources). You will need to complete and return this to the UK Identity and Passport Service along with the required travel documents. If your passport was simply damaged, send the passport to IPS when you apply for a replacement. It will be returned to you once it has confirmed your identity and that the damage was not due to fraudulent tampering.
Request and complete a new passport application form from ISP (see resources) and prepare to submit the following: a photocopy of your current photo ID, your full UK or British Overseas Territories birth certificate, and two identical color passport photos 4.5 by 3.5 centimeters in size. They must be a frontal portrait of the face taken against a white background and without any glasses or anything worn on the head.
Call the UK Identity and Passport Service at 0300 222 0000 between the hours of 7 a.m. and 11 p.m. to file a request for a replacement passport. It will have you send your forms, required documents and damaged passport (if applicable). The fee for an adult passport is £77.50 for standard service and £112.50 for the one-week expedited service. A child passport costs £49 for standard service and £96.50 for the one-week expedited service. One-day service is not available for replacement passports.