As both SK and AC are in Star Alliance, you may be able to get your boarding passes issued at ARN which removes this problem altogether.

However, you MUST clear security at LHR (but not passport control etc), so if they cannot issue BPs in ARN, on arrival follow signs for T3 connections, go through security and back into the lounge. In the far left corner, all the T3 airlines have transfer counters. At this point you can get your new BP, then go back out into the gate area.

1hr is cutting it a bit fine though - remember you can end up waiting 30 mins for a gate...