There was a similar scheme for people such as yourself called the Registered Teacher Programme (RTP) but I'm not sure if it still exists. To do that you only needed to have 240 credits and (like the GTP) were employed as an unqualified teacher whilst training. Perhaps you could check with the TDA to see if it is still running - though numbers were always much lower than the GTP. I really don't think you will get onto a GTP without an honours degree. Perhaps you could get additional credits through the OU?