Best traditional Sunday roast/London?

Planning another trip to London in fall, and really want to experice the ultimate prime rib/beef Sunday meal.

Walked by (and have heard about) Simpsons in the Strand...looks and sounds great.....and have heard of Rules (are they more known for game?)..

Anyway, any suggestion would be greatly appreciated. Old world atmosphere a plus....

Ate at Simpson's about 20 years ago, and it was great. Very old fashioned atmosphere, very proper preparation of prime rib, yorkshire pudding, etc. I can't imagine it's changed much? They are all about tradition there, I thought.