Mr Optimistic
Just to confirm that when I was working in the 13x9 and the spinning tunnel (RIP) in 1954 it was joining Little Staughton and Thurleigh that had been considered for a long runway.
Twinwood is south of Thurleigh so not in a suitable direction. The cutting to which you refer was connected with the ability to taxy aircraft to the tunnel site for use with a possible blower tunnel facility like the one at Boscombe.