The Conservatives have extended their lead over Labour as pro-Brexit voters return to the party, according to the latest Opinium poll for the Observer.

Despite a week of political chaos that has seen Boris Johnson purge the party of 21 MPs who oppose his plans, the Tories recorded a 10-point lead over Labour. For the first time since March, more than half (53%) of leave voters now intend to vote Conservative. Almost half of all voters (46%) now think the Conservative party has in effect become the Brexit party.

The polling will be used by Johnson’s team as evidence that their ruthless strategy to push hard to secure Brexit and hold an election can work. However, the strategy has run aground as opposition parties are blocking an election from taking place.

The Conservatives are up 3 points to 35% of the vote, while the Brexit party is down 3 points to 13%. The Liberal Democrats are up 2 points to 17%, with Labour down 1 point to 25%.

Opinium said there was a considerable amount of voter churn, with only the Lib Dems retaining an overwhelming proportion of their vote from the last election (83% of 2017 Lib Dems would vote for the party again). Both the Conservatives and Labour are on track to lose votes to the Lib Dems among their remainer wing and lose votes to the Brexit party from their leave wing.

For the first time since the 2017 general election, Opinium said it was recording a direct shift in votes between the two major parties. Just over a fifth (22%) of Labour leave voters are now intending to vote Conservative.

Johnson’s personal ratings have been dented after his bruising week in the Commons. Now only just over a third (36%) think he would be the best prime minister, down from 41% last month. However, Jeremy Corbyn is not benefiting from Johnson’s troubles. Only 16% say he would be the best prime minister.

Only 37% approve of the way that Johnson is handling the Brexit process, while 43% disapprove. However, that is better than than the ratings for Corbyn. Just 17% approve of the Labour leader’s response, and 20% approve of Jo Swinson’s.

Johnson’s decision to prorogue parliament has not upset leave voters. The public as a whole is divided on this: 33% support the prime minister’s prorogation of parliament, while 36% oppose it. This is split evenly along EU referendum lines: 59% of leavers support the prorogation, while 61% of remainers oppose it.

Adam Drummond, the head of political polling at Opinium, said: “We’re facing unprecedented times in Westminster, and it’s very difficult to predict what will happen in the next few days, let alone further beyond. While Boris Johnson isn’t garnering much support from the public, he does at least remain ahead of his closest rivals, and more than double the amount of people approve of the way he has handled Brexit compared with Jeremy Corbyn.

“The reason for these numbers is that Boris Johnson has invited the clear disapproval of remainers on Brexit, in return for the clear backing of leave voters. On the other hand, opposition leaders have managed to unite leave voters in disapproving of their response to the government without succeeding in wholeheartedly winning over remainers.”

Opinium polled 2,009 people online from 4-6 September.