Another 10 players will go - some, possibly next week - as Ashton builds towards revealing the 30 players entrusted with making England's Webb Ellis Trophy defence in France during September and October.
And second-row forward Borthwick, out of the England scene since last year's RBS 6 Nations, desperately wants to be in the mix.
He said: "In 2003, the (England) team was pretty much written in.
"There weren't that many places to be decided, whereas there is a different situation this time around.
"I am determined to make it, and I believe I am in the best physical condition I've ever been in.
"I am confident I can mix it with the best in the world in terms of my skill levels, and I am in great nick."
England will fine-tune their World Cup preparations by facing Wales and France (twice) on successive weekends next month, and Borthwick added: "I am just hoping that Brian gives me a chance in these August games.
"I missed out in our big success in 2003, so this World Cup is huge for me."