His opportunity to test his electoral strength there came in 1786, when the Earl of Surrey, sitting member and leader of the opposition to Lonsdale there, succeeded as Duke of Norfolk and vacated his seat.
The 1790 British general election there was riotous, marked by mob violence that led to the destruction of Lonsdale's townhouse.
Knubley and James Clarke Satterthwaite, the Lonsdale candidates, were returned with 503 votes each, over the incumbent John Christian Curwen and fellow independent Wilson Braddyll with 399 and 394.
This disenfranchised the honorary freemen created at Lonsdale's direction, and Knubley and Satterthwaite were unseated in favor of their rivals.
After a strenuously-contested fifteen-day poll, Curwen and Fletcher-Vane emerged the victors, and a petition against them by Knubley and Graham was rejected.
At the time of the 1790 general election, Knubley expressed his opinion of Lonsdale to Boswell: "a most tyrannical temper and not a spark of gratitude."