I would keep it relatively simple, with everything on the fast lines paired on a half-hourly pattern:
4ph calling at Milton Keynes only
2ph continue to Wolverton, Northampton then all-stop to Birmingham
2ph continue along the Trent Valley (1ph fast to Chester/North Wales and 1ph stopper to Crewe)
4ph calling Watford, Milton Keynes, Rugby
2ph continue fast to Coventry/Birmingham/Wolverhampton then on to Shrewsbury/Scotland
2ph continue semi-fast along the Trent Valley (1ph to Manchester, 1ph to Liverpool)
2ph calling Leighton Buzzard, Bletchley, Milton Keynes
Both continue to Wolverton, Northampton and then maybe extend to Coventry or Nuneaton