Is it possible to apply for a Schengen visitor visa with my South African passport whilst in the UK? I am the partner/married to a UK passport holder & citizen.
It depends on how long you are in the UK.
To apply for a Schengen visa from the UK you must be a UK resident for at least three months. If this condition is not fulfilled, the Consulate of your country of preference will hardly take the application into consideration.
Non-residents such as travelers and tourists who plan on staying in the UK for 3 months or less should be discouraged from applying for a Schengen visa from within the UK. Instead, they should apply in their home country so that the application is processed, chances of getting a positive answer become greater.