I finally got round to trying the 'leave the bhajis for 8 hours after their first cook' idea. And I must say I was very pleasantly surprised. I cooked them in the morning for only a couple of minutes to get the batter set and a slight golden colour, then the went on a plate in the cupboard (room temperature) for the rest of the day. At curry time they got another quick dunk in the hot oil to heat through.
The was much more mushy on the inside and there wasn't any hint of rawness to them. the outside was nice and crisp with a lovely fried onion taste. Cooking them like this also ensures none of the spices got burned at any time either.
It sounds fairly obvious now I have tried it. Every BIR in the country pre cook their bhajis, normally at least half a day, sometimes 36 hours ahead of their useage. Everyone should give this a go and see what a big difference it makes.