According to Realtime Trains the route and timings were;
<p>Cardiff Central [CDF] 1.......1555.........................1555........................RT
Marshfield............................1602.........................1602........................RT
Ebbw Junction....................1604 1/2...................1605 1/4..................RT
Newport [NWP]...................1607 1/2/1609 1/2..1608 1/4/1610 1/2....1L
Maindee West Junction....1611...........................1612 1/4.....................1L
Llanwern West Junction...1613..........................1614 3/4....................1L
Severn Tunnel Jn ..............1618 1/2....................1620 1/4....................1L
Severn Tunnel West..........1619 1/2....................1621............................1L
Severn Tunnel East............1623.........................1624 3/4...................1L
Pilning [PIL]...........................1624.........................1625 3/4...................1L
Patchway [PWY]..................1628.........................1629 1/2....................1L
Bristol Parkway [BPW].......1630/1633...............1632/1640...............7L
Westerleigh Junction........1637 1/2...................1644..........................6L
Hullavington........................1644 1/2...................1652.........................7L
Wootton Bassett Jn...........1651..........................1658..........................7L
Swindon [SWI].....................1657 1/2/1700.........1704/1706................6L
Uffington (Oxfordshire)......1708.........................1714...........................6L
Challow.................................1709.........................1715...........................6L
Wantage Road....................1711............................1717 3/4....................6L
Steventon.............................1713 1/2....................1719...........................5L
Milton Junction...................1714 1/2....................1719 3/4....................5L
Foxhall Junction.................1715 1/2....................1721...........................5L
Didcot Parkway [DID]........1716 1/2/1720..........1722 1/2/1724 1/2...4L
Didcot East Junction.........1721...........................1724 3/4...................3L
Moreton Cutting.................1722.........................1724 3/4...................3L
Goring &amp; Streatley .............1726 1/2...................1729 1/2...................3L
Reading High Level Jn......1732..........................1734..........................2L
Reading [RDG].....................1734/1736................1735/1737 3/4..........1L
Kennet Bridge Junction....1738..........................1738 1/2...................RT
Twyford [TWY].....................1741...........................1742...........................1L
Maidenhead [MAI]..............1744 1/2...................1744 1/2...................RT
Slough [SLO]........................1747 1/2...................1747 1/2...................RT
Stockley Junction...............1750 1/2...................1751..........................RT
Heathrow Airport Jn..........1751...........................1751 3/4...................RT
Hayes &amp; Harlington ..........1751...........................1752...........................1L
Southall West Junction.....1751 1/2....................1752 1/2..................RT
Southall [STL]......................1752.........................1753...........................1L
Southall East Junction......1752.........................1753...........................1L
Hanwell Bridge Loop........1752 1/2...................1753 1/4...................RT
Hanwell [HAN].....................1753..........................1753 3/4..................RT
Acton West..........................1754..........................1754.........................RT
Acton Main Line [AML]......1755.........................1755 1/4...................RT
Friars Junction....................1755 1/2...................1755 3/4..................RT
Old Oak Common West...1756.........................1756 1/4...................RT
Old Oak Common East.....1756 1/2...................1756 3/4..................RT
</p>
London Paddington ..........1804.........................1806 1/4...................2L
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