Is it against the law for hotels to allow animals to stay on the premises, UK?

When looking to book a hotel or B&B for holidays in England it very often announces "pets welcome". I assume this to mean live animals. Surely this is against the law? I would have thought that persons with pets would go for caravan or chalet holidays where pets would be left outside in a shed, cage or kennel as they would at their own homes? This is very frustrating when one sees a special good holiday offer and then sees that pets are encouraged.