Alison Bright-Thompson

Alison Bright-Thompson (AUDIO: The Keys of Baker Street) was the mother of Robin Bright-Thompson and the partner of Ken Bright-Thompson.

She met Ken in a blind date in the 1990s somewhere on Baker Street. Both Ken and Alison became very involved in their careers, so that all three were rarely in the same place at the same time. (AUDIO: The Keys of Baker Street) While Ken and Robin lived in 107 Baker Street in 2020, she could not join them as she worked abroad, though she was on the lease. (AUDIO: Lost Property)

Later, Mr Bird called a residents' meeting in Baker Street, noting that "Mr and Mrs Bright-Thompson are out, as per usual". (AUDIO: Must-See TV) By the time Ken and Robin left Baker Street, in an alternate world, she had never set foot in their new home, though the location had been selected as a way for her and Ken to "recapture the past", close to where they'd first met. (AUDIO: The Keys of Baker Street)

In one alternate timeline in which Alison and Ken never met, since Ken had instead taken a liking to Liv Chenka, Robin Bright-Thompson never existed. Since he had become involved in a whole network of alternate timelines, intervening across his own time stream, this put the whole multiverse in a state of collapse, only repaired when Robin and the Doctor worked together for a second chance.

Finally, in the newly stable timeline, the Bright-Thompsons didn't break the lease and leave Baker Street early in 2020. (AUDIO: The Keys of Baker Street) move out of Baker Street early in 2020. (AUDIO: The Keys of Baker Street)

Behind the scenes
In Lost Property, while citing the paperwork for the Bright-Thompsons' acquisition of a flat in Baker Street, Helen Sinclair refers to her as "Ms Bright-Thompson", while Must-See TV has Mr Bird referring to her as "Mrs Bright-Thompson". Which title she goes by isn't entirely clear. However, since the former is from an official document, and given Mr Bird's later-to-be-revealed identity, this seems more likely to be the one.