The UK's hotel industry has a genuinely strong pet-friendly reputation, especially outside the largest cities, where countryside coaching inns, historic hotels and boutique properties often actively market themselves as dog-welcoming. That said, there's no single national standard — policy, fees and restrictions are set by each property individually.
Fees range from nothing at all to a flat one-off charge per stay, occasionally scaled by the number of pets or the length of stay. Weight or breed limits are less common in the UK than in some other countries, but do appear, especially at smaller boutique properties with limited room sizes.
Always confirm three things directly with the property before booking: whether there's a fee and how much, whether specific rooms or floors are pet-designated, and whether dogs can be left alone in the room (many UK hotels explicitly prohibit this, even briefly, for noise and liability reasons).