Why does my Hotpoint TDL30 dryer decide to run at a slow speed?

My Hotpoint Aquarius TDL30P dryer should run clockwise then anti-clockwise but lately, instead of reversing after running for a few minutes in one direction, will decide to continue to run in the same direction but at a lower speed. The heating element will then start to get too hot as the fan is also running slowly. Any ideas on what's gone wrong and how to fix it?