Ty, you don't say whether you're trying to preserve some/all of the original paint (I hope you are - see Major Nichols comments further down). If so, I have had good results with a non-corrosive product named EvapoRust. There are some nuances in its use, so if you want to give it a try, contact me off-list and I'll share my thoughts. The main thing is to start out conservatively with soaking time. Shorter soaking time removes less rust, but does not soften the paint too much. When I've gotten it just right, the paint and chrome are preserved but the rust is gone. Here's a link to their website:
http://www.evaporust.com/
EvapoRust does not leave any residue (the frame or parts should be thoroughly rinsed after soaking), so it does not prevent future rust - be ready to touch up with primer within a couple of days.
It's a little cumbersome soaking an entire frame (and it takes gallons of the stuff, which can get expensive). So I use the big "paste" trays that wallpaper hangers employ in their trade to soak one tube at a time. You can get them (depending on your locale) at a big-box store like Home Depot, OSH, etc. or a to-the-trade paint supply store.
Now, regarding Major Nichols. You may already know just how rare your frame is (only about 60 recorded). There is an enthusiasts' group for the marque, based near MN's former home and shop (he passed away in 2005). Like many small British makers, his bikes are prized among the lucky few who own them (and hardly anyone else knows anything about them!). I'm fortunate to have one of his track frames, with the original paint. Here's a link to a website with more info on MN, in case you don't have it:
http://www.blackcountrysociety.co.uk/
Alvin Smith, the main MN mover and shaker, may be able to help you with restoration advice if you're so inclined.
Good luck with your project. If you live anywhere near me, I would love to see it in person.
Regards,
Dave Ross
Portola Valley, CA USA
shaping up to be a lovely day for a ride