Plaid Cymru secured an overall majority on Gwynedd County Council , north-west Wales, as a result of two by-election triumphs.
Its candidate Mandy Williams-Davies gained at Diffwys and Maenofferen from the Voice of Gwynedd group and the party defended the Penrhyndeudraeth seat.
There was disappointment for Labour in conference week with its vote share dropping in the only two comparable contests, leaving it trailing Tories by 2.7% in a nationwide projection based on 10 by-elections over the month.
Liberal Democrats defended marginal seats against Conservatives at Bishop's Castle, Shropshire and Nascot in Hertfordshire's Watford Borough.
A calculation based on nine by-elections in September fought by all three major parties both times gives a line-up of: C 40.5%, Lab 35.6%, Lib Dem 13.9%.
Cherwell District - Bicester North: C 443, Lab 130, Lib Dem 99. (May 2011 - C 1,013, Lab 432, Lib Dem 275). C hold. Swing 6.4% Lab to C.
Gwynedd County - Diffwys and Maenofferen: Plaid Cymru 210, Voice of Gwynedd 153. (May 2008 - Voice of Gwynedd 247, Plaid Cymru 206, Lab 48. (July 15, 2010 by-election: Voice of Gwynedd 185, Plaid Cymru 181). Plaid Cymru gain from Voice of Gwynedd.
Gwynedd County - Penrhyndeudraeth: Plaid Cymru 515, Voice of Gwynedd 233, Ind 91. (May 2008 - Plaid Cymru 577, Voice of Gwynedd 409). Plaid Cymru hold.
Shropshire County - Bishops Castle: Lib Dem 801, C 544, Lab 80, Green 74. (June 2009 - Lib Dem 754, C 641, Green 186). Lib Dem hold. Swing 4.9% C to Lib Dem.
Watford Borough - Nascot: Lib Dem 1,021, C 818, Lab 134, Green 133. (May 2011 - Lib Dem 1,285, C 1,023, Lab 328, Green 179). Lib Dem hold, Swing 0.2% C to Lib Dem.