It's a long read mate, but worth it if you want a detailed take on the issues around this.
It is broadly as described elsewhere; the private companies to take the easier, profitable work, and let the NHS deal with the expensive, difficult stuff.
It might get people treated faster, which is always a good thing, but it certainly doesn't make things cheaper for the NHS overall (and quite possibly, the opposite).
Circle’s lawsuit against an NHS CCG illustrates the flaws in financially comparing private and NHS providers.
chpi.org.uk