Severely curtailing domestic flights is not a realistic option. The rail network does not have the capacity to absorb all the passengers currently flying. It would need additional tracks on the major trunk routes - that is just not feasible in a country where available land is so restricted (particularly in the south-east). The French have built an impressive TGV network, but it has been on completely new tracks. The new Channel Tunnel Eurostar link is all we are likely ever to see.
For the last 20 years I have travelled frequently between Scotland and the South of England. I used to fly sometimes but drive more frequently. After some terrible road journeys I vowed never to drive again to Scotland. For the last 10 years I have flown and occaisionally used the train. I tried driving again a few months ago and quickly realised it was a mistake. North of Manchester was no problem but had numerous delays in the southern part of the journey in both directions. I was totally frazzled by the end. The rail journeys have generally been reasonably on time but the big problem is overcrowding. Eeven if I have a reserved seat I am often hemmed in by lots of people standing/sitting in the aisles. On average the rail fare is twice what I would have paid by air.
So for me I will continue to fly and hope that the present and future governments do not tax domestic air travel excessively. There is just not a viable alternative.