curious delay on view/where

Hi folks.

I have the following view:

CREATE VIEW "stock_available" as  SELECT * FROM stock_details  WHERE available = true AND visible = true AND location
notin (SELECT descr FROM ignored);
 

Stock_details is itself a view pulling in a number of tables. Everything 
works fine until I try to pull in only the details for a specific 
branch, using the following.

select * from stock_available where branch = 'Leeds';
or
select * from stock_available where branch = 'Doncaster';

At this point, the query takes 11 seconds. Any other quiery, including

select * from stock_available where branch != 'Doncaster'
and
select * from stock_available where branch != 'Leeds'

which only return the equivelent of the top two (we only have Leeds and 
Doncaster) are les than  1 second.

Anyone got any ideas of the cause, or thoughts on how I can trace the 
problem?

-- 
Gary Stainburn
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