Some of the growth will just naturally come from there being trust in there being a stable government for the next 10 years. Add in that the country will no longer be losing as much money to corruption, and there will just be some natural, inherent growth that's been choked out by the Tories.
Other growth will be triggered just by spending on the basics. If you get more money in the pockets of working classes, they instantly spend it because it's actually really hard emotionally to save when you've been struggling. Whether this is a big night out, on a new fridge when the old one is almost but not quite dead, a nice outfit, or whatever, if money gets into the pockets of people who've been skint and tight, it'll get spent and chain into more growth.
I think after Labour's first budget, regardless of what's in it, there'll be a starting point for some growth. My fear is largely that they don't utilise it enough to turn the spending taps on and trigger more.