The 2 Conservative gains in Washington were the first time the party had won seats in the town since it became part of Sunderland council.
Stewart-Sandeman's victory was the first recorded Conservative gain of the election.
The Conservative gains took the party to 22 seats, compared to 48 for Labour.
This was the first Conservative gain in a by-election since 1982.
Both seats were Conservative gains from Labour at the 2010 general election.
Also the best Conservative gains in a generation and the worst Labour result since Michael Foot.
From 1997 until a Conservative gain in 2010, Labour won the contests with safer margins.
During the 2011 assembly elections he unexpectedly lost his regional list seat, due to Conservative gains at constituency level.
His was one of only four Conservative gains in that election.
The result followed the Conservative gain of the Greater London Council in the elections the previous year.