Here is the polling graph from pollsters Redfield & Wilton of the so-called Red Wall seats (seats that had been held by Labour for decades but which switched to Conservative in the 2019 general election):
A year ago (September 2022), Labour was polling 61% in the Red Wall, which pretty much guaranteed them winning dozens of seats. Labour has lost 16 points since then and are now at 45%.
Reform, a party to the right of the Tories, are now at 10% (they are the aqua blue line at the bottom of the graphic).
Tory hopes of retaining the red wall involve squeezing the Reform vote, hence Suella Braverman's speech on illegal migration.
Note that while a lot of polls are showing strong support for Reform in the 6% to 10% range, in recent by-elections, Reform has struggled to get above 3%.
The next by-elections are Rutherglen and Hamilton in a week's time, and then a by-election in Tamworth and another in Mid Bedfordshire in three weeks time. Let's see if they also follow the pattern of a depressed Reform vote. If so, that should cheer the Tories up, especially if they manage to hold at least one seat.