customs will definitely seize them if caught do not attempt to do trade within eu countries
they even can Prosecute you
...
Nope, you won't get prosecuted for buying cigs, unless they can prove that you intend to re-sell them.
If the customs seize the parcel, they'd ask you to pay the duty on it, and if you choose not to, they'll destroy them. That's it.
@OP, £6 per pack is a lot. "Standard" under the counter price for these is £4.5 - £5.