I have a couple more. Maybe a Milton Keynes Central to Carmarthen via Northampton calling at Milton Keynes Central, Northampton, Rugby, Coventry, Birmingham International, Birmingham New Street (spilt), 1. Rowley Regis, Stourbridge Junction, Kidderminster, Droitwich spa, Worcester Foregate Street (connect), Malvern Link (alternate service), Great Malvern, Colwall (alternate services), Ledbury, Hereford, Abergavenny, Pontypool and New Inn (alternate services), Cwmbran (alternate services), Newport, Cardiff Central, Bridgend, Port Talbot Parkway, Neath, Swansea (reverse), Llanelli and Carmarthen.
Another could be a Liverpool Lime Street-Salisbury via Oxford. It could call at Liverpool Lime Street, Liverpool South Parkway (alternate services), Runcorn, Crewe, Stafford, Wolverhampton, Tame Bridge Parkway, Birmingham International, Coventry, Leamington Spa, Banbury, Oxford, Didcot Parkway (alternate services and reverse), Swindon, Chippenham, Trowbridge, Westbury and Salisbury.
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Also another could be a South to North train from Dover Priory to Aberdeen. It could call at Dover Priory, Ashford International, Tonbridge, Redhill, Guildford, Reading, Oxford, Birmingham New Street, Derby, Sheffield, Wakefield Westgate, Leeds, York, Darlington, Newcastle, Edinburgh, Haymarket, Inverkeithing, Kirkcaldy, Leuchars, Dundee, Abroath, Stonehaven and Aberdeen. This could just be once daily in each direction.