Here's a wild guess. Sinnock Square is near to Croft Road (at least according to the Foyle's War web site!
http://www.foyleswar.com/locations/brigitte2.htm).
According to Chris in 1066 Land's website (
http://www.rootschat.com/history/hastings/content/view/10/49/):
A piece of land in the croft was given as a site for a meeting house for Independents in 1805, but as no local tradesman dared to erect such a structure, a wooden building was made in London and brought down by sea. The Croft Chapel was later built on the same site but was pulled down in 1972 to build flats.
According to
www.a2a.org.ukRemarks and Observations made by Mr Richard Sinnock, on his own Conduct and Gods dealings with him; both in Providence and Grace, through a long series of Years: being spared to the advanced Age of 82 Years on the 6th day of December 1822
[from Administrative History] Richard Sinnock began a cordwaining business in Hastings in 1762, but moved to London in 1785 in order to join a dissenting sect, and subsequently to Guildford. In 1799 he moved to Battle where he built a new house adjoining the Baptist church which he attended. He was active in promoting the founding of an Independent congregation in Hastings which culminated in the building of the Croft Chapel in 1805, for which he provided the land. When there was a split in the Battle congregation, Sinnock remained with the fifteen representatives of the original Baptist Church (see also NU3) and services were frequently held in his house. This group flourished and in 1821 a new meeting house called Zion Chapel was built on land given by Sinnock
Therefore, it may not be unreasonable to surmise that Sinnock Square was either named after Richard Sinnock or his family. Unfortunately, I don't have any details of Richard's parents.
Regards
Mark
