waivar,
There probably are a few. The sort who believe in service, duty and that sort of thing (usually reservists or ex-service , I gather - can you imagine Gordon Brown going off to serve in Iraq as a TA officer? Blair? er.. no). Problem is, because the politician of that ilk is invariably not a self-serving 'sh-one-t' [to use Jane Clark's description of Alan], they rarely rise to prominence.
If you really want to be depressed at the low calibre of most politicians, read Jeremy Paxman's book 'The Political Animal' - a damning indictment on the self-interested idiots that populate the benches of the Commons.