Here is an article (borrowed from the Shirley Association website) that discusses a couple of theories regarding the origin of Saswallo, who is occasionally referred to as a possible progenitor of the Sewell/Sewall families:

Castellan of Lisle

Notes on the Descendancy of the Family of Ensor
By Peter Lee
Nuneaton & North Warwickshire Family History Society -
If you visit the village of Ettington in
the south of the county of Warwickshire,
you will find a nineteenth century
mansion that was once the seat of
the Shirley family. Indeed the manor
and the previous house had been in
their family for over 900 years. The
building today is one of England's
grandest hotels. Engraved on a stone
wall is lettering which reads:
"When good St. Edward wore the
crown/ Saswallo here was thane:
His male stem this manor own/ Now
in Victoria's reign"
There are other families who have
claimed descendency from Saswal[l]o
including the families of de Etwall, de
Mungei, de Snitterton and Ible, De
Pecco, de Alfreton, Ingleram, de Ireton
and de Ednesour (from whom the
current family of Ensor now under
review are all descended) - but who
was Saswalo?
The Shirleys believe he was a Saxon
nobleman who for some reason benefited
under the largesse of William the
Conqueror. I beg to differ and here is
the reason. A book entitled 'The Norman
People' published in London
1989 reads : "Shirley: This family descends
from Sasualo, who held vast
estates from Henry de Ferrers 1086.
He had been supposed of Anglo-Saxon
origin, but the name does not occur
amongst the proprietor's t. Edward
Confessor (Domesd.); nor is it probable
that such vast estates (nine
knight's fees) would have been given
to an Anglo Saxon. The name is
probably foreign. Sasualo or Saswalo
was Castellan of Lisle (Keeper of the
castle of L'Isle - or the island - now
Lille in Northern France but then) -
Flanders c.1000 and 1039 founded the
Abbey of Palempin (Albert Miraeus,
Op. Diplom. i. 54) His son, Robert,...

Does any of this ring a bell with anyone?

David Sewall
Maine USA