Mailing gear ahead in the UK? Insurance?

So I'll be touring around Great Britian for three weeks this spring, and will be doing an 8-day backpacking trip along Hadrian's Wall.

I'll have a small but heavy bag of stuff (a netbook, a UK guidebook and some other things not needed/wanted on the hike) and am trying to figure out how to get it from one side of England (Newcastle upon type) to the other (Carlisle).

This little packet will be very valuable (mainly due to the netbook) and so I need to choose a carrier that offers good insurance and has reputation for not losing stuff. Yes I know there are baggage transfer companies along the Wall, but they are expensive and most seem to have a 2-bag minimum.

Who do I choose? I could not find any info on insurance at the Royal Mail website. There is also DHL and UPS. Can any Brits out there suggest which to choose?

My opinion is simply based on logic...You gow ith the largest most reputable companies you can find...UPS, Fedex, DHL...they ALL should offer you insurance...there is easy tracking as well...