finding text in a string

I am trying to find records where the post code starts with a certain set of characters from some 10,000 records, 1300 or so of which meet the select below. My code is

Select * from table where mid(postcode,1,2 ) IN ("CV DE LE MK NN")

This returns a zero result A typical postcode would be something like CV1 9AD

If I write

Select * from table where mid(postcode,1,2 ) = "CV"

I get the full list of records for post codes beginning with "CV" I would have thought that the IN statement would work. Can anyone tell me why it does not?