Who is the only female British athlete to have won Olympic, World, European and Commonwealth titles?

Sally Gunnell.
She won Gold in Barcelona Olympics 1992, In the World Championships in Stuttgart 1993 and European Championships in Rome also in 1993.

I believe this is Sally Gunnell:

Olympic - 1992 Barcelona Gold 400m hurdles

IAAF World Cup - 1993 Stuttgart Gold 400m hurdles

European Championships - 1994 Helsinki Gold 400m hurdles

Commonwealth - Multiple golds listed below:
1986 Edinburgh - 100 m hurdles
1990 Auckland - 400 m hurdles
1990 Auckland - 4x400 m relay
1994 Victoria - 400 m hurdles
1994 Victoria - 4x400 m relay

Also European Cup gold medals:
1993 Rome - 400 m hurdles
1994 Birmingham - 400 m hurdles
1996 Madrid - 400 m hurdles
1997 Munich - 400 m hurdles

and European Indoor Championships gold medal
1989 The Hague - 400 m sprint


https://en.wikipedia.org/wiki/Sally_Gunnell