Eurolines United Kingdom
There are bus connections between the United Kingdom and Norway. You’ll find more information on:

By bus to Rena
Østerdals-ekspressen drives between Oslo and Trondheim and stops a few times a day in Rena.
Travelling time from Oslo to Rena is 2 hours and 50 minutes. From airport Oslo Gardermoen travelling time is 2 hours and 5 minutes.

Usually it is not necessary to book bus-rides ahead of time. You just pay the driver as you board.