Someone on the GR board asked who Anne K's next 'target' in the GB all-time list was and the only players I could think of were Wade, Barker and Durie, all of whom peaked in the top 5. Turns out someone on tennisforum.com has tried to list all players who have ever appeared in the top 100 by country in the open era, and lists the following for GB with their career highs.

It's clearly not entirely accurate (e.g. most sources give Sue Barker's career high as no. 3 and Annabel Croft's as 21 and the TF post gives 4 and 24 respectively) but it's as complete as we're likely to get! If I come across any more corrected values or sources, I'll update them.

GREAT BRITAIN : 13 players

Virginia Wade (2 - 3 Nov 1975 - source ITF)
Sue Barker (4? - 20 Mar 1977 - source ITF (*))
Jo Durie (5 - 29 Apr 1984 - source ITF)
Winnie Shaw (10 - early 1970s - TF only)
Michelle Tyler (22 - source TF only, would have been in the 1970s)
Annabel Croft (24 - 31 Dec 1985 - source WTA, other sources plus Wikipedia say 21 at the same date)
Anne Hobbs (33 - 30 Nov 1981 - source WTA)
Sara Gomer (46 - 26 Sep 1988 - source TF/Wikipedia)
Monique Javer (56 - ITF says CH 704 (!) I'm sure she was higher than that!)
Samantha Smith (57 - 17 Aug 1998 - source ITF, TF/Wikipedia say 55)
Anne Keothavong (61 - 10 Nov 2008 - source WTA)
Sarah Loosemore (76 - 1993 - source the Times)
Clare Wood (77 - 2 May 1994 - source WTA)

(*) most Sue Barker bios say 3 and she herself has said that she was ranked 4 in 1976 before she won Roland Garros, which suggests that even if she didn't reach no. 3, she reached no. 4 before the date given on ITF.

Edit: There turns out to have been a Winnie Shaw who played in the 1970s too.

In essence then, going on this measure, Anne will be one of the top 10 GB players in the open era if she takes out Sam Smith's career high, or Monique Javer's depending on which source has got Sam Smith's CH correct.