Virgin West Coast Trains operates a train from Milton Keynes to Hyde Park Corner every 30 minutes. Tickets cost $30 - $55 and the journey takes 32 min. London Underground (Tube) also services this route every 5 minutes.
From Milton Keynes Central train to Euston Underground Station, Tube to Green Park Underground Station, then walk to Hyde Park Corner. 49 min £35. From Milton Keynes drive to Hyde Park Corner. 1 h £10. From Milton Keynes rideshare to London then walk to Hyde Park Corner. 1 h 46 min £6.