If you lose your passport while you're away, you should cancel your passport as soon as possible to reduce the risk of anyone else using your passport or your identity. You can do this online here: https://www.gov.uk/report-a-lost-or-stolen-passport.
You should contact your travel provider to see if you will need an emergency travel document in order to travel home. It is likely that you will and to obtain one you will need to contact your nearest British embassy, high commission or consulate. You can find out more information on Gov.UK's website.
You can make a claim for the cost of extra transport, accommodation and administration costs you have to pay to get a replacement passport or emergency travel document - we will pay up to £500 towards these costs.
Please keep all receipts and obtain written confirmation from the embassy / consulate showing the date of the incident and cost of the replacement passport.