Pet-related fees across UK accommodation generally fall into the same three categories found elsewhere in Europe: a one-time cleaning fee, a per-night or per-stay charge, or a refundable deposit. Which one you'll meet depends heavily on the type of property — cottages and self-catering lean toward a flat one-off fee, while hotels more often add a per-night charge instead.
Refundable deposits are relatively uncommon in mainstream UK pet-friendly accommodation compared with some other countries, but do appear at higher-end properties, or where a listing has had previous issues with pet damage.
Always get the figure confirmed in pounds sterling and in writing before arrival — a fee quoted verbally over the phone, especially at a smaller family-run property, can sometimes differ from what actually shows up on the final bill if it wasn't pinned down in advance.