Have to agree with previous posters. If you go into 1st on a Standard ticket and do not upgrade BUT use the Wifi provided then you are technically breaching the NRCoC in respect of using a service for 1st class on a standard ticket without the appropriate fee being paid.
Now would the TM/Guard do anything? Potentially not. But s/he could do if they really wanted.
I know this happened on another operator and the guard took exception and removed the passengers off the train. (Which is the guards right - S/he can cite the reason "You do not fit the requirements to travel today") the passenger complained. The operator replied saying that they stole the wifi and they were breaching the NRCoC and the wifi terms.
Is it really worth it? When the wifi is rubbish for most of the journey..