Hello Stephen,
the Atlas Code 55 Track is intented for the use with american rolling stock, which got RP25 wheels. I made the same mistake on my first british layout, where I wanted to use Atlas code 55 track. My entire locos stalled at the turnouts. (Dapol 14xx, GraFar 3F and 4F. The Peco and Farish Wagons run well on the Flextrack, but have some problems on the turnouts, The Dapol wagons hit the ties, when running.
When you are using british/continental rolling stock, it is better to use Peco Code 55 tracks.
Markus