The Politwoops website says "Even politicians post things they regret later. You can see the tweets they posted first, and deleted after on Politwoops."
There is also an EU version.
There is some hidden gold in there and it's a useful resource for journos and no doubt not admired by politicians aware of it. Tweet as an MP but it will never be erased.
Tweet in haste repent forever.
The Twitter feed is - @deletedbyMPs