So... what happened to the £29.99 price?

I checked out the game on Steam this morning and it was showing at £29.99. Went to buy after work tonight and it's up to £39.99. I thought I'd imagined it, but the steamprices site for PA does show it was £29.99 for a while.

Did I miss some kind of limited-time offer, or was it a glitch?

Most likely a Steam Conversion glitch/issue.

probably a glitch. the current price for beta is supposed to match what the backers paid for beta.
Just like how the alpha was $90 (not sure of UK conversion), to match the backers who paid for it. (price gradually dropped as alpha came to a close.

Bummer, £29.99 felt about the right price point for me. More waiting.

The current price for Beta is not supposed to match anything from the KS campaign. The packages for Beta and Retail that are sold through the Uber Store were never tiers during the KS. There was however and $40 and $50 tier that included Beta access.

It's was glitch like low price in Russian Steam on start of alpha.