The 'other' solution is given on the DFT site:
http://www.dft.gov.uk/pgr/rail/pi/highspeedrail/alternativestudy/pdf/railintervention.pdf
The rail paper is quite interesting it proposes a number of packages, such as:
-Replacing London Midland Desiro fleet with 125 mph capable rolling stock
-Grade-separation between Cheddington and Leighton Buzzard,
-Extra 3 new platforms at Euston and
-Extra platforms at Manchester (with grade separation at Ardwick),
-4 tracking Attleborough Brinklow (including freight works at Nuneaton),
-Northampton area speed improvements
-4 tracking Berkswell Stechford (Coventry corridor)
-New Moor Street platforms (WCML route)
in addition on the Chiltern line
-Electrification throughout (including replacement of existing Chiltern clubman diesel rolling stock)
-125 mph maximum line speed
-New chord from Chiltern Coventry corridor (avoiding Coventry but including new Coventry South station)
- Banbury cut off (includes to Kings Sutton) IE new line around Banbury
- Improvements at Princes Risborough
- New 2 track tunnel Saunderton Seer Green (avoiding High Wycombe)
- 4 tracking of Seer Green South Ruislip (Northolt Junction)
- 2 tracking of South- Ruislip Paddington (via Park Royal & Old Oak Common)
- Possible new Paddington - Birmingham express (4 tph) with 1 hour journey time
The paper does mention the GCR, but it is not looked at, though it could I suspect be re-opened as far as Leicester fairly easily. The paper discusses the maximum the WCML can be upgraded - there's not much more can be done with it because of problems with train length. After that the solution is to price people off.
Overall, a fairly largish capacity increase with the Chiltern upgrade, but no realistic journey time reductions. If Labour pull out, we are most likely to end up with the above.