Can you get minecraft free on PC?

Not legally, but even then you can only play on certain (crowded) servers.
Buy Minecraft, it's only £20.

No. All attempts to purchase codes from unofficial re-sellers on forums will cause your account to be banned. And all free downloads only let you play a single-player mode, or hacked lobbies.

Technically, yes you can get Minecraft for free. BUT the account isn't free. As long as you are logged on to minecraft.net on your PC that you will download it on, it's free. You only need one account to download Minecraft on multiple places.