I think Bletchley had an hourly Manchester service before Milton Keynes Central, but I don't think it's had a regular intercity service since then.*Do any Avanti services stop at Bletchley?
*I can't remember if LNR's Crewe services call there on Sundays, and Bletchley had the LNR Euston – Northampton – Birmingham – Liverpool services when they briefly existed, but they're not really intercity ones.