“Do you have evidence that she was working then? Maybe you can share it with us.”
Sometime likely in late in 1961 or early to mid 1962 she she may have acted in her earliest two BBC TV episodes in the UK. This is my estimate based on the usual delay between shooting shows and the shows being broadcast. It is a guess. There may be much more accurate information in the BBC archive as to when her scenes were shot...perhaps as early as August 1961. Sometimes the whole season is shot before the season starts.
Here is a link to her filmography and the two shows:
http://www.imdb.com/name/nm0765586/filmogenre
BBC Sunday-Night Play: Season 3, Episode 43
Sword of Vengeance (29 Jul. 1962)
The Avengers: Season 2, Episode 13
Death Dispatch (22 Dec. 1962)
I haven’t found what she was doing before that and where.
The Avengers: Season 2, Episode 13
“Death Dispatch”
Filming begins: 22-Jun-62
Filming completed: 23-Jun-62
Released London: 22-Dec-62
http://www.dissolute.com.au/avweb/season2/213.html
This was the 4th episode shot for season 2. Most were shot within a month of broadcast. It was the first episode filmed with Honor Blackman as Cathy Gale.
http://www.dissolute.com.au/avweb/season2/index.html
The Sunday Night Playhouse would have been on a much tighter schedule because they broadcast every week of the year.