Londoners or recent visitors....What is a large department store in London that is very similar to Harrod's?

There's not many left if you don't count the chains like John Lewis and Debenhams. Selfridges in Oxford Street has a Sushi bar on the ground floor. It has recently had a makeover and has lost a lot of its early 20th century charm

From the mid 1950's thru the 1960' and into the 1970's, Harrods had such a department employing more than 50 staff including vets and zookeepers. You could by a variety of wild zoo animals form zoo's in the UK and Europe, most of the pets for sale were of linage that dated many generations born in captivity. They even sold an elephant and big cats were both popular and legal on the streets of London until 1976 when passage of the Endangered Species Act, effectively ended the practice. However, the King's Road area was home to several exotic pet shops in the 1960's as well, and it was perfectly normal and accepted practice to see a stylish young London woman accessorize her go go boots, mink coat, and bouffant hair with a lion cub on a leash.

Selfridges has a sushi bar on the Ground Floor, it's in Oxford Street near Bond Street Station.

Selfridges - they have a Yo Sushi in the food hall on the ground floor

Are you thinking of Selfridges?