This paper investigates the impacts of possible measures to enhance HSR market share in the London-Amsterdam market. To this aim, we adopted a two-level aggregate nested logit model able to jointly model trip distribution and trip generation, thus taking into account that the tested policies may increase or decrease the overall demand. The model was applied to an extensive dataset about passenger flows traveling between London airports and HSR station and Amsterdam in the period 2015–2019. The results show that both the reduction of HSR fares and the application of an air ticket tax, albeit with different impacts in terms of stimulus or reduction effect on overall demand, are ineffective in increasing HSR market share, if not adequately supported by improving HSR service. Increasing HSR frequency and reducing HSR travel times constitute the best opportunities to increase HSR ridership by stimulating a higher substitution effect than modifications in relative fares. Lastly, the recent queueing at airports, following staff shortages and strikes, significantly lower air transport demand and potentially has a substantial upward effect on HSR market share.