Literally, "to have form" means to have a criminal conviction, to be on police records. In this case, under a previous Labour government in the 1970s, the British economy became incapable of sustaining itself by its own efforts and had to call on the International Monetary fund for a large bail-out, which was accompanied by stringent conditions.

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Note added at 6 mins (2009-01-31 17:12:43 GMT)
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Before being applied to criminal convictions, I believe this term came from horse-racing.