I adapted Yurt's DS1's school's trick with the crisp and the baked beans. Had a tiny piece of ham in one hand and a crisp in the other. I said ' DS2, first try ham, then crisp' . After a couple of times when he put it in his mouth and spat it out again, he actually chewed and swallowed it (making horrible faces). Finally he ate it voluntarily - the first new thing he's eaten for two years! Don't think it's his favourite food (in fact it was a bit like watching a bushtucker trial ) but he he did it! Also tried it with pear (which he used to eat but went off) and had success again. Now i just have to remember to keep going with it.
So thanks Yurt