Liberal Democrats gained from the Tories in the latest council by-elections, taking a marginal seat in the Maidenhead constituency of Home Secretary Theresa May.
Their candidate Simon Werner triumphed by eight votes at Pinkneys Green in Windsor and Maidenhead Royal Borough. The ward's councillors are split between the two parties.
Conservatives also failed at South Oxfordshire District when Labour easily defended a knife-edge marginal at Didcot All Saints.
Labour was also boosted by analysis of eight comparable results this month which suggest a projected 8% nationwide lead for the party over the Conservatives - up on the 7% margin in a survey for the BBC of May's main polls.
A calculation based on six wards fought both times by all three parties gives a line-up of: Lab 38.3%, C 31.4%, Lib Dem 15.3%.
The only other result where a seat changed hands this week was at Hartlepool Borough.
The Putting Hartlepool First group gained from independent at Seaton in a contest where the three major parties polled barely a third between them.
Tories did manage to comfortably hold on against an independent at St Marys, Fenland District, Cambridgeshire where they previously had a majority of just 40 votes.
No more by-elections are reported until November 15, the same day as police commissioner polls in England and Wales.
Caerphilly County Borough - New Tredegar: Lab 692, Plaid Cymru 95, C 24. (May 2012 - Two seats Lab 965, 744, Ind 362). Lab hold.
Fenland District - St Marys: C 397, Ind 160, Lab 78. (May 2011 - C 364, Ind 324, Green 104). C hold.
Hartlepool Borough - Seaton: Putting Hartlepool First 441, Lab 261, Ind 193, Ukip 128, C 94, Lib Dem 31. (May 2012 - Three seats Ind 1168, 883, 769, Putting Hartlepool First 328, Lab 287, 274, Ukip 243, Lab 237, Putting Hartlepool First 172, C 158). Putting Hartlepool First gain from Ind. Swing 4.3% C to Lab.
South Oxfordshire District - Didcot All Saints: Lab 436, C 340, Lib Dem 151. (May 2011 - Two seats Lab 647, C 642, 635, Lab 597, Lib Dem 226, 185). Lab hold. Swing 5.7% C to Lab.
Windsor and Maidenhead Royal Borough - Pinkneys Green: Lib Dem 839, C 831, Ukip 152, Lab 121. (May 2011 - Three seats C 1338, 1239, Lib Dem 1248, C 1234, Lib Dem 1045, 999, Lab 316, 259, 228). Lib Dem gain from C. Swing 3.5% C to Lib Dem.