Veterinary costs in the UK are high by international standards, and a standard consultation is only the entry point — a genuine emergency, especially one involving surgery or overnight hospitalisation, can run into the thousands of pounds quickly. This makes travel pet insurance a reasonable thing to check or arrange before a UK trip, even for owners who've never needed it domestically.
If your existing pet insurance is domestic-only from your home country, check specifically whether it extends to veterinary treatment received in Great Britain — some policies limit cover to the EU or to a specific list of countries, and the UK, being outside the EU, may need a separate travel add-on or an explicit confirmation that it's included.
Keep the policy documents and an emergency claims number somewhere accessible that doesn't depend on a single device staying charged. Most UK policies, like elsewhere, expect you to pay the vet directly and claim reimbursement afterward, so budget for the upfront cost regardless of what the policy ultimately covers.