I have to say, this didn't work. I think the problem was twofold. Partly my crappy combination oven (still waiting to get my decent one back from my sister), and partly because I didn't have a roasting tray/dish, so I improvised with my casserole dish as I only had 6 Toulouse sausages.
The batter did rise to some extent, but the bottom just didn't get hot enough, even though I had it on a hot stove before returning it to the oven with the batter and sausages. So, the top burnt, and the underneath wasn't cooked enough, and I ended up having to return it to the over for a while longer on a lower heat to try and get it all to cook. I'll know next time.
The gravy was great though, so although the toad was a bit disappointing, the gravy and mash made up for it. With this, I half cooked the sausages in the oven with a coarsely chopped red onion, Dijon mustard and a little extra oil. Then I used the onions and oil and fat from the sausages as the basis of the gravy.