>>1853358>>1853361They could have at least kept the trainshed, the 60s one is appalling.
My solution to the small great hall issue would have been to do what they ultimately did at King's Cross decades later: rotate the location of the entrance concourse by ninety degrees relative to the whole station, converting the old great hall into a cocktail bar, hotel or just a fancy waiting area. If the Euston Road underpass has to be extended to make room, so be it. Even if some demolition has to take place, the great hall being (as you say) relatively small should have facilitated its retention.
At the very least, there was no need to demolish the Euston Arch.