First, in the UK, the following novels are definitely available as deadtree books:
In The Mouth of the Whale
Gardens of the Sun
The Quiet War
Five titles from my back list - Four Hundred Billion Stars, Eternal Light, Red Dust, Pasquale's Angel, and Fairyland - may still be available as paperbacks, but are I think mostly out of print.
All of the above are also available as ebooks in the UK. The rest of my back list as at present out of print, but I have plans to revive several titles as ebooks.
A short story collection, A Very British History, was published by PS Publishing in March, and is very much in print. And a single-volume anthology of the Confluence trilogy, with two associated stories tipped in, will be published by Gollancz in December.
In the US, only Gardens of the Sun, The Quiet War and Cowboy Angels are available as deadtree books. (Three other titles are still under contract with Tor, but have long been out of print, and haven't been turned into ebooks because, amongst other reasons, Tor have a vast pre-ebook-era backlist.) They are also available as ebooks - but as I discovered, they aren't available as the British versions. That's because I have a different publisher, Pyr, in the US, and while Gollancz was briefly able to release its ebook versions in the US, that ended when they sold US rights to Pyr. And that's why, I'm afraid, the price of The Quiet War hasn't dropped in the US: it's a special offer on the British ebook associated with a new novel coming out from my British publisher.
The five back list titles mentioned above are available as ebooks in the US, by the way, because I took back the rights after they went out of print in the US, and offered them to Gollancz. If you're confused at this point, I don't blame you.
Availability of books still reflects the old territories carved out by publishers in different countries. British publishers claim the UK and most Commonwealth countries; US publishers the US and Canada. Back in the day, US readers would not have expected US editions of books to reflect the pricing of editions in British bookshops. Now that the internet connects everyone with everyone else, it isn't much of a stretch to imagine that someone in the US should be able to download a British edition of an ebook; but rights and territories, and the geolocatory vigilance of platforms like Amazon, prevent that.
Neither In the Mouth of the Whale or Evening's Empires have a US publishing deal. At present, if American readers want to buy either novel, I can do no more than point them towards the Book Depository, which sells deadtree books with free worldwide shipping. And if they want the ebook versions, then I'm afraid it won't be possible (outwith spoofing your location) unless and until an American publisher buys the rights, or until Gollancz decides it can't sell them.
However, there are a few other ebooks which are available in both the US and UK (and in Canada and elsewhere). These are titles I published myself to Kindle Direct, including the stories 'City of the Dead'[, 'Dr Pretorious and the Lost Temple', and 'Prisoners of the Action', the short story collection Little Machines (originally published by PS publishing), and two collections of Quiet War short stories, Stories From The Quiet War and the latest, published just last week, Life After Wartime.