UPDATE:
Hottest of the new discoveries is Jacob Andrew Tarttelin, who was the father of one of the William Tarttelins, and we believe he was OUR William’s daddy, but this does need more examination. Jacob was born about 1751. He was a mariner. At the time of his death he was living on a boat in Kings Lynn and his burial record of 1813 suggests that he came from SWEDEN. Whilst he almost certainly wasn't from Sweden, it does indicate the name may well have come over from Europe, which casts uncertainty on the previous version below ...
The name Tarttelin is pretty uncommon. I have yet to go somewhere and bump into a Tarttelin I haven't met before. I am regularly asked if I have Italian or French parents. I didn't get any conclusive information from my Dad about it's origins, so when I saw someone at Wookey Hole advertising his surname researching services, I set him onto our name.
I wound up at Wookey Hole during my Honeymoon, and as my wife Freya had only just acquired the new surname, it seemed appropriate to find out more about it. We didn't get any immediate feedback, other than it was nice to have a challenge, rather than just another Smith or Jones.
After a little more than 3 months, and a couple of calls to find out whether he had forgotten or just given up, we got a plaque back with the details. According to him, the surname originates from the parish of Tarleton in Ormskirk (a few miles North of Liverpool). Over the centuries, the spelling has been copied down wrong, until the name morphed into Tarttelin, with William Tarttelin being the first known registered Tarttelin.