There is no problem in going either from Hethrow or Gatwick. But may be while coming depending upon your visa status. You need to get college/uni letter mentioning your status of studies, especially when your course finishes. If you have other type of visas, they ask nothing but if you don't and ready to raise hands........no more asylum thesedays rather deport because illigal immigrants are expected to be near about a million in UK. Enjoy nice journey!!!!