'A Dictionary of British Surnames' by Reany, Routeledge, Keegan, Paul, 1958. has this to say about the Cruttenden name:

Cruttenden - William Crotynden 1451 PAT (K) A Kent and Sussex name from a lost place Cruttenden in Headcorn (Kent). Pat Calender of Patent Rolls (in progress).

English Placename Society Vol 25 - English Placename Elements has this to say about the derivation of place name endings:

denn - woodland pasture, Old English, Kent dialect.

Thus originally there might have been a fellow by the name of 'Crutte' who kept his pigs in a clearing in the wood (den). Later when surnames were developing a resident from nearby this woodland pasture who went to live elsewhere may have been known as 'Cruttenden'.

There is another theory that the original place name was derived from a cross in a valley. Local Old English crucdenu 'Valley with a cross' Kent 15th cent.

I am not convinced that the Cruttenden name is in any way connected with the Druids. In pre-Christian Celtic society they formed an intellectual class. The earliest Classical references to Druids date to the 2nd century B.C.

From the late 15th century there is no doubt that the origin of the Cruttenden name is firmly based in the south-east of England around the borders of Kent and Sussex. That is in one of the first areas of the British Isles to be colonised by the Anglo-Saxons from the 4th century AD onwards. Previous to this there had been over 400 years of Roman rule.

Another theory of origin concerns the clan system in Scotland. As there is no evidence of the use of the Cruttenden surname in Scotland before the arrival of Cruttendens from Kent/Sussex in the mid 19th century this theory must also be discounted.