Stuck in gear

Set off to church this morning on the bike. Got halfway down the road and realised it would not change above second gear. All sorts of thing crossed my mind as I stopped at the garage. I had a look and assumed it was ice as it seemed to have eased. I continued on to Church and it seemed to be fine. On the way back it started out OK but it became stuck in forth. I went the long way home to avoid any sharp turns and made it home. After a good look its seems as if the gear lever had become stuck due to either dirt of corrosion. Good application of oil and things seemed to be OK. Took on a short ride out with plenty of gear changes just to confirm it. Will have to keep an eye on this.