I was running up the stairs and twisted weird, now my knee feels like it's going to lock when i bend and it's painful do i need to see my gp?

Get an exam.: Certainly couldn't hurt to have a doctor examine this. Could be something simple, but I'm concerned inasmuch as the knee generally doesn't like torque - that twisting motion that you described. This could lead to some degree of internal trauma which could be uncovered by a good physical exam of the knee and perhaps some directed testing if deemed necessary.

See a specialist: If possible, see a specialist in orthopedics. This could represent a meniscus (cartilage) tear, a sprain of the capsule, a minor subluxation of the patella, etc. For now, ice x 20 minutes 3-5x/day and limit your weight-bearing until you can see a physician.