Betty in 1951 at the Festival of Britain. Note the gorgeous railings. More info from Ben:

“She was one of many boats acting as riverbuses for the festival of Britain in 1951 .  She was licensed in the 100-200 passenger category and was owned by R.F Jackson at the time. “

Big thanks to Ben from Liquid Highway for finding and emailing it.

Based on this I have found out a few more little fact-ettes… From an article about City Cruises:

“The core of the initial City Cruises fleet in 1989 came from Thames Tripping (Westminster) who supplied Eltham, Westminster and Witheycombe.Mayflower Garden came from River Functions (Thames). The various “Rose” boats of Thompson Launches joined City Cruises from 1993. The Thompson Brothers had acquired their first boat, St Patrick, in 1929, and put her on the Westminster to Tower service. Thompson Launches Ltd was incorporated in 1935. The Beta III joined their fleet in 1959 from Jackson Bros.“