Hey, thanks so much for these responses Emma and Flora.
Both of you are correct in your take on how things should be handled - been up half the night working on it - but I could have gone to sleep early and just read your posts.
I had an 'Aha!' at Flora's third way. The Ed had written a ref to 'TSP' in his email as well, so here they are:
http://www.ipgbook.com/
It's an interesting idea, UK publisher distributes UK book in states as a foreign right.
I've earned out my advance, so it'll be interesting to see what they come back with.
I would argue that my former agent should improve the deal in our favour as a trade for assigning those rights but as he didn't even get the title right in the first contract it's highly unlikely.
I'm going to do a bit of research on reserves against returns though, as per Curtis's book, and see if there isn't a way to get US royalties paid straight through on that element.
Also be interesting to see if there's an e-book element to the contract. I'm holding out for 50/50 splits as per NUJ guidelines rather than the Big Publisher driven 25/75.
***
Just called the Society of Authors - who are all very sore from their Christmas party yesterday (which explains why I couldn't get hold of anyone). Their take on it was that it was often handled as another foreign right at 10% of net receipts. They made another point though: push for short lifespan of license 3-5 years max.
It such a shame this has to go through my old agent, I could have had the chats with the publisher already and nailed this down rather than having to play with the piggy in the middle.
Thanks so much for your replies. Writewords subscription earned back already!