olney - wolverton/mkc (wcml ) or bedford (mml)
towcester - milton keynes (wcml ) or banbury (chiltern)
dunstable - luton (mml) or leighton buzzard (wcml)
Cambourne - St Neots (ECML) or Cambridge
Wells/Shepton Mallet - Bath or Castle Cary
Olney - Wolverton and MK are closer than Bedford.
Towcester - Northampton's closer than Banbury or Kings Sutton so doesn't count as same line as Milton Keynes or Wolverton (which is closer to Towcester than MKC)
Dunstable - closest stations are Leagrave and Luton - Leighton Buzzard's much further out.