The Liberal Democrats are increasingly confident they can beat the Conservatives in large parts of southern England, including the two Oxfordshire seats formerly held by David Cameron and Boris Johnson. Ed Davey, the Lib Dem leader, spent Sunday campaigning in Bicester, where the party believes it can defeat the Conservative candidate, Rupert Harrison, a highly regarded economist and one-time adviser to the former chancellor George Osborne. Davey’s visit was part of a strategy that has seen the party roam further into safe Tory territory as the campaign has gone one, buoyed up by polls that show it picking up support across large parts of the south and south-east. A party source said: “We’re really encouraged by what we’re seeing in the final stretch of the campaign. Tory support seems to be collapsing in southern England and we’ve continued to pick up support.” The party went into the election focused on 80 seats where it finished second in 2019 – almost all Tory held. Officials say more of those 80 are now in play than when the campaign first began. “Canvass returns are looking better than they were a week ago, and even better than they were two weeks ago,” said one. Internal Lib Dem polling seen by the Guardian suggests there will be close races in Bicester and Woodstock, Didcot and Wantage, Henley and Thame – which includes much of Johnson’s former seat – and Witney, Cameron’s old constituency. The party believes each of these could be won by a margin of just 500 seats. This tallies with national polls that suggest the party has picked up more than one percentage point during the campaign, while the Conservatives and Labour have shed support. Large-scale MRP models suggest every pollster expects the party to win Henley and Thame, but they are split over which party will win the other three Oxfordshire target seats. The party will spend the final days of the campaign targeting Labour voters in seats where Labour finished third in 2019, hoping they can unlock as many as 25 seats in a final frantic effort. As well as the Oxfordshire seats, the party is pouring resources into Theresa May’s former seat of Maidenhead, as well as the south-western seats of Frome and East Somerset, and Torbay.