If you have a mobile phone, then considder upgrading to this one:
Motorola Defy Plus... basically a waterproof, shock proof, dust proof scratch resistant Android Smart phone with built in class 12 GPS... can be had for £170 sim free or £14 a month on contract!
With MemoryMap for android or ViewRanger loaded onto the phone it's easy to follow routes and switch between normal road SatNav and OS map routes..
Quote:
Overview of Motorola DEFY Plus watch the video
http://www.somobile.co.uk/motorola/defy+plus/ 
The Motorola DEFY Plus is the follow up to the Motorola DEFY, the highly popular 'Lifeproof' smartphone.
The DEFY Plus maintains the design of its predecessor but has a bolstered specification, which includes a 1GHz processor and Android 2.3 Gingerbread.
Resistant to dust and water, the DEFY Plus has an IP67 protection rating. Corning Gorilla Glass also ensures that the 3.7" display is scratchproof, providing peace of mind when you're out and about with your phone.
The DEFY Plus is the same size and weight as the original DEFY, but does come equipped with a higher capacity battery of 1700mAh. The 5 Megapixel camera is improved slightly as well, featuring auto focus, flash and digital zoom.
The connectivity features of the DEFY Plus are as you would expect, with Wi-Fi, Bluetooth, 3G and 3.5mm audio jack all present. Internal storage weighs in at 2GB, but up to 32GB of storage is available via microSD expansion.
Features of Motorola DEFY Plus
■Android 2.3 Gingerbread
■1GHz Processor
■IP67 Protection Rating, Water resistant, dust resistant
■Scratch Proof 3.7" Corning Gorila Glass Display
■5MP Camera
■Wi-Fi, Bluetooth, 3G
■3.5mm Audio Jack
■MicroSD expansion up to 32GB, 2GB Internal Storage
What's in the box of the Motorola DEFY ?
■Motorola Defy Plus
■2GB MicroSD Card
■Stereo Headset with mic
■MicroUSB Data Cable
■AC Adapter (UK)
■Battery 1700mAh
■Supporting Documentation
..
Buy a handlebar mounted Box & Charger for it: So you can fix in a handlebar mount for your phone AND a hardwire charger for it running directly from your battery or headlamp power feed
http://stores.ebay.co.uk/GPS-For-LESS/MOTORCYCLE-ACCESSORIES-/_i.html?_fsub=1138798012&_lns=2&_sid=349105992&_trksid=p4634.c0.m322But there are plenty of others and an Otterbox defender with a handlebar mount (AND and additional safe cable for any major offs) is a best option..
Then load ViewRanger onto the phone with the whole of the UK on OS mapping (& France now)...
ViewRanger will work with MemoryMap routes..so you can down load MemoryMap routes or plan your own on MemoryMap or the various web sites that have OS mapping on line for free...
ViewRanger now have their own on line route planning web page...
http://www.viewranger.com/en-gb/route-plannerViewRanger..
http://www.viewranger.com/en-gbVideo
http://www.youtube.com/watch?v=B64slQ-YjBk&feature=player_embeddedMemoryMap...
http://www.memory-map.co.uk/
The software might look daunting to begin with but once you have done it..it's simple...
NOTE:
I use ViewRanger on an old android mobile and MemoryMap on the PC..
However since ViewRanger came out and was so good..MemoryMap have brought out their own mobile phone software that I've not yet seen in action but will probably buy when I upgrade my own mobile to a DEFY+

(You need MM v5 for it to wwork though...)
http://shop.memory-map.co.uk/acatalog/iPhone_iPad_Apps.htmlhttp://www.memory-map.co.uk/supportforum/viewtopic.php?f=56&t=4695http://www.memory-map.co.uk/downloads/PDF/MMV5-INST-QSG-APP-1%20iPhone%20&%20iPad%20QSG%20-web.pdfSo the advantage is that you have a mobile phone that is robust enough, especially with an additional bar mounted box, to use on the trails in ALL weathers...
as well as a: GPS that can be used as a normal SatNav on the road bits and OS mapping GPS on the trails.
as well as a: Water proof, shock proof and dust/scratch resistant 5Mp camera AND decent Video camera that you can then use to download photos and vids to a ride report WITH a GPS route... (although plan well to avoid using only legal routes..)