Many thanks to all that gave advice.

I have now removed the dust cap, undone the one shot nut and drifted out
the old bearing. This was a one piece sealed for life type (£27.50) and
comes complete with dust cap, new nut and circlip. I have taken it into
a local engineering works to have it professionally pressed into the hub
(£2). It will be ready this afternoon. Under 30 quid doesn't seem too
bad.

Fortunately the otherside seems OK and the trailer has only done about
200 miles since new, but it looks like one of the seals failed on this
bearing and having stood for 12 months gave it the opportunity to
corrode significantly.

I will be taking a spare bearing kit with me and if I do not need to use
it during the trip (god willing), I will have the nearside bearing
changed after I return.

Once again many thanks to all who responded.

Regards, Eddie.