What is needed is trains of a sensible length, rather than Voyagers.
One possible solution is to split (short term until electrification) the XC services so that they run Manchester to Coventry by 8 coach EMU's (110mph) and south coast by Voyagers up to Birmingham Airport.
If nothing else it would provide better capacity along that core, however it will also free up at least four Voyagers for use elsewhere to strengthen services.
Potentially allowing all the services between Manchester and the South Coast to be run as a single Voyager to Basingstoke, a pair of Voyagers to Birmingham international with the northern section being run by EMU's between Coventry and Manchester.
That would mean that XC could then focus on NW to SW to provide capacity on those services.
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Of course if the existing Manchester to south coast services are run by 221's then, if my suggestion is carried out, then they could be run by 220's (doubed up between Basingstoke and Birmingham international).
That would mean that the services previously run by 220's would then be run by 221's, which would provide them with a little more capacity.
It would also reduce the number of DMU's running through New Street.