Isn't inflation 17%? I don't think they could campaign on matching that for the public sector because it might be impossible to follow through on. When you're in Opposition you really don't have much idea what the finances are like till you get in power. Unless he's going to commit to very substantial tax and NI increases at the same time, which seems unlikely. There's a while til the election so I wouldn't rule it out.
I read a thing ages ago that said the public actually want quite left wing policies like nationalisation, higher taxes, higher NHS pay, they just don't trust left wing governments to administer them. Which is why Starmer tries to look a bit like a Tory, I suppose.