Ukip triumphed against Tories in the latest by-elections with its third council seat gain in the bandwagon started by the Eastleigh parliamentary contest.
Candidate William Harness won at Humberston and New Waltham, North East Lincolnshire, where he had come a close second in last year's polls.
His victory will add to pressure on Conservatives just four weeks ahead of the main polls for English counties and unitary authorities.
Ukip came second at Bilborough, Nottingham, and Pemberton, Wigan.
Meanwhile, the Liberal Democrats missed breaking Labour's monopoly of councillors at Knowsley Borough, Merseyside, by 38 votes at Prescot West.
Analysis of six comparable contests this week suggest a 9.1% projected nationwide Labour lead over Tories.
A calculation based on just four wards fought both times by all three major parties gives a line-up of: Lab 40.3%, C 28.3%, Lib Dem 16.4%.
Tories may have been helped by the fact that in three wards their vote share was already so low that there was a limit to how far it could shrink further.
Knowsley Borough - Prescot East: Lab 515, Lib Dem 328, C 47. (May 2012 - Lab 976, Lib Dem 505, C 51). Lab hold. Swing 4.8% Lab to Lib Dem.
Knowsley Borough - Prescot West: Lab 441, Lib Dem 403, Trade Unionists and Socialists Against Cuts 86, C 62, Green 14. (May 2012 - Lab 819, Lib Dem 667, Trade Unionists and Socialists Against Cuts 172, C 101). Lab hold. Swing 2.4% Lab to Lib Dem.
Knowsley Borough - St Michaels: Lab 676, Lib Dem 69, C 44. (May 2012 - Lab 1497, Lib Dem 116). Lab hold. Swing 4.3% Lab to Lib Dem.
North East Lincolnshire Council - Humberston and New Waltham: Ukip 1098, C 738, Lab 470, Lib 311. (May 2012 - C 1231, Ukip 1001, Lab 596). Ukip gain from C. Swing 10.9% C to Ukip.
Nottingham City - Bilborough: Lab 1542, Ukip 347, C 176, Green 103, Lib Dem 96, Elvis Loves Pets Party 31. (May 2012 - Three seats Lab 2573, 2407, 2288, C 824, 780, 763, Lib Dem 421, BNP 381, 379). Lab hold. Swing 9.4% C to Lab.
Nottingham City - Woollaton East and Lenton Abbey: Lab 627, Lib Dem 368, C 116, Ukip 75. (May 2012 - Two seats Lab 981, 942, Lib Dem 676, 631, C 551, 530, Ukip 79, 54) Lab hold. Swing 4.0% Lib Dem to Lab.
Wigan Borough - Pemberton: Lab 1084, Ukip 451, Community Action Party 203, C 89, BNP 63. (May 2012 - Lab 1996, Community Action Party 291, C 205). Lab hold. Swing 9.6% Lab to C.