Large spa town in Gloucestershire; headquarters of GCHQ (10)

I believe the answer is:

cheltenham

(Other definitions for cheltenham that I've seen before include "West Country spa town with racecourse" , "Gloucestershire racecourse" , "here near the Cotswolds" , "Gloucestershire town" , "English racecourse and spa town" .)

I've seen this clue in The Mirror.

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