Here are some recent opinion polls, from Wikipedia:
I've highlighted in blue where Reform are ahead of the Tories, and in green where the two parties are neck and neck. So far there have been 3 polls with Reform ahead, and another 3 where they are equal.
Immediately before the election was called, the Tories were polling 10-15 points ahead of Reform. So what's changed?
Firstly, Sunak has had a bad campaign. He started off badly by announcing the election outside Downing Street in the rain, and got wet:
He compounded this by leaving the D-Day commemoration event early, making him look uncaring, incompetent and un-Prime-Ministerial. I mean, all he had to do was look solemn and get photographed with other world leaders, how hard would that have been?
Then Nigel Farage took back the reins of his Reform UK party from interim leader Richard Tice. Farage is more charismatic than Tice, so their popularity went up.
But the underlying problem for the Tories is simply that after 14 years of their rule, people don't like them. People on the left don't like them because their policies have systematically made the least well off 50% of the country poorer in order to help the top 1% (their rich friends). People on the right don't like them because they have vastly increased immigration, both legal and illegal, and have failed to do anything to combat wokism. And normies don’t like them because Johnson broke his own lockdown rules, and Truss’s budget massively increased their mortgages.
Most people don't think much about politics, except during elections. Because people are thinking about politics more, they are increasingly thinking they don't like the Tories.
What will happen next?
The Tories are almost certain to lose most of their seats (they won 365 in 2019). They'll probably go below 100 seats and in the worst case may get under 50 seats and be pushed into 3rd place (behind the Lib Dems) or 4th place (behind the Lib Dems and Reform). People on Manifold think there's a 24% chance Reform will get more votes than the Tories. I would put the probability slightly higher than that, at 30-40%.
After the general election, there will be a Tory leadership election. Whoever wins it will then have to do something about Reform. There will be great pressure for the Conservatives and Reform to merge. Maybe they'll call the new merged party the Reformed Conservatives?
"Most people don't think much about politics, except during elections. Because people are thinking about elections more, they are increasingly thinking they don't like the Tories". Well put!
The whole Reform vs the Tories thing; even if they don't formally overhaul the Tories electorally they have already warped their political thinking to be basically indistinguishable anyway. I'm kind of reminded of the last line of Animal Farm:
"The creatures outside looked from pig to man, and from man to pig, and from pig to man again; but already it was impossible to say which was which."