OSLO, Aug 10 (Reuters) - Norway"s centre-left opposition parties are expected to defeat the incumbent Conservative-led coalition government by a two-to-one margin in next month"s election for parliament, a new opinion poll showed on Tuesday. The Sept. 13 vote could thus end Prime Minister Erna Solberg"s quest for a third consecutive term and instead give Labour Party leader Jonas Gahr Stoere a chance to negotiate a power-sharing agreement with left-leaning groups. Widely praised last year for a swift coronavirus lockdown, giving Norway one of Europe"s lowest COVID-19 mortality rates, Solberg nevertheless faces a backlash over economic inequality and public sector reforms that have proven unpopular. In April the prime minister was fined by police for breaking social distancing rules at her birthday gathering, further damaging her standing. read more The Conservatives and smaller parties on the centre-right look set to win 55 seats in the 169-member assembly, down from 88, while the centre-left could grow to 114 from 81, the survey showed. The Aug. 2-6 poll by the Kantar agency for independent TV2 comes just as the election campaign kicks off and confirms a downwards trend shown in earlier polls. Campaigning on a slogan that it is now the "common people"s turn", Labour promises tax relief for low and middle income families, an end to privatisation of public services, more money for hospitals and a tax hike on the top 20% of incomes. Norway"s Green Party is also set to boost its presence in parliament, as is the far-left Red, and both will seek to influence a Labour-led government. Adding to the complexity, Centre leader Trygve Slagsvold Vedum has declared himself a candidate for prime minister, rivalling Stoere, although his party now polls around 16%, lagging Labour"s 23.5%. A growing rural-urban divide, in which many voters objected to the reorganisation of police, healthcare and municipalities, in many cases centralising key functions, has been a boost for Vedum, who got just 10.3% in 2017.