There had been widespread speculation that Mid Bedfordshire MP had been contemplating a move to UKIP.
However, it is understood the Ukip issue did not come up at her meeting with Sir George this afternoon, which was described as "convivial".
Ms Dorries said: "I am delighted. It is long overdue."
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An unsettled day with rain and blustery winds. Brighter and colder by the afternoon.
Increasing cloud and rain overnight. Blustery and cold tomorrow.
Events are taking place in Cambridge, Norwich, Colchester, Southend and Lowestoft today, to mark Holocaust Memorial Day.