Ferries are the other main sea route into Great Britain for pet owners, running Channel crossings (Dover–Calais, for instance) and longer North Sea routes from the Netherlands and Scandinavia. Pet policy is set operator by operator rather than standardised across the industry, so it's worth checking the specific company's current rules directly before booking rather than assuming they match Eurotunnel's.
On the shorter Channel crossings, pets typically stay in the vehicle for the duration, the same as on Le Shuttle. Longer overnight sailings on North Sea routes sometimes offer pet-friendly cabins instead, letting the pet travel with you rather than in a vehicle deck — a genuinely useful option if your route is long enough to need an overnight crossing anyway.
Whichever operator you choose, the pet travel documentation requirement is the same as for any other route into Great Britain: microchip, rabies vaccination, Animal Health Certificate, and tapeworm treatment for dogs, checked against the specific ferry route and crossing time you've booked.