Here's what I did:
First problem is that there are no line-breaks in the file, and all the xml elements run together. Snipped example:
<trkpt lat="54.0936185326" lon="-1.4954326954"><ele>28.98</ele><time>2013-05-25T15:44:36Z</time></trkpt><trkpt lat="54.0936553292" lon="-1.4953642990"><ele>28.50</ele><time>2013-05-25T15:44:37Z</time></trkpt>
So using notepad++, I used the Search / Replace function in 'extended' mode to replace '><' with '>\r\n<' to give this format:
<trkpt lat="54.0505749453" lon="-2.1588976309">
<ele>207.30</ele>
<time>2013-05-25T08:12:53Z</time>
</trkpt>
<trkpt lat="54.0503291041" lon="-2.1592391934">
<ele>205.86</ele>
<time>2013-05-25T08:12:56Z</time>
</trkpt>
Now, look at the end of the file:
<trkpt lat="54.0936553292" lon="-1.4953642990">
<ele>28.50</ele>
<time>2013-05-25T15:44:37Z</time>
</trkpt>
<trkpt lat="54.0938047785" lon=
The last valid trackpoint is shown, along with the final incomplete one.
I deleted the incomplete trackpoint.
Now, to close out the un-matched XML elements.
Look at the top of the file, there are 3 things which have been started, but don't have their corresponding close tags at the end of the file - <gpx>, <trk> and <trkseg>:
<?xml version="1.0" encoding="UTF-8" standalone="no" ?>
<gpx xmlns="http://www.topografix.com/GPX/1/1" [....] >
<metadata>
<link href="http://www.garmin.com">
<text>Garmin International</text>
</link>
<time>2013-05-26T08:05:54Z</time>
</metadata>
<trk>
<name>2013-05-25 08:58:26 Day</name>
<extensions>
<gpxx:TrackExtension>
<gpxx:DisplayColor>DarkYellow</gpxx:DisplayColor>
</gpxx:TrackExtension>
</extensions>
<trkseg>
[...]
So at the end of the file, I close them out, adding the 3 lines at the bottom:
<trkpt lat="54.0936553292" lon="-1.4953642990">
<ele>28.50</ele>
<time>2013-05-25T15:44:37Z</time>
</trkpt>
</trkseg>
</trk>
</gpx>
Then I saved it as <filename>.gpx.