>fingers not that nimble (stylus?)
>do I want an Android tablet or a smartphone
>ease of use
>good battery
>under GBP 100
>Support for Geocaching
First off, I'm remembering the backpacker's saying - an ounce going out in the morning is a pound coming back in the evening. I'm going to assume you are having a wonderful easy walk, not climbing through 1000's of feet of vertical ups and downs, and that a few ounces of weight will be of no concern, otherwise recommendations would change.
Next I'm assuming you have Internet access at home for your Windows PC and are not charged based on how much data you use per month. Ideally you have WiFi at home too. (which will enable cordless file transfer between your existing PC and this new device.) Otherwise you will use a USB cord between the device and the PC. Alternatively to Internet connectivity at home you can take your device to any free WiFi hot spot, library, most McDonalds, etc.
You have gone a long time without a cell phone or smart phone so perhaps an "all in one" solution might be ideal? I'm going to recommend a 7" phablet (combo of phone & tablet), with GPS capability.
* Does all you require above
* at 7" its easy to see
* has a quality touch screen so no need for a stylus
* very bright display for outdoor use
* could be used as a cell phone (recommend you start with a low cost, prepaid plan - about 5 cents per minute for calls and no surprises)
* always free to use in any WiFi area
* the GPS system is free to use any time
* fast (as in fast map manipulation, fast GPS fix calculation, etc.
* can do a LOT more than just geocacheing and recording ways
* can easily be used with a windshield mount as a car GPS
* over time should be a LOT of fun
At 7" its a bit "clunky" as a cell phone however it will fit in a large/loose man's pants pocket.
Remember all you need for geocaching are maps that you download and install at home, a charged up battery, and a CLEAR VIEW of the sky. You don't need to be "near a town" for it to work. However with ANY GPS you cannot be under a very heavy canopy of trees. A clear "line of sight" to the sky, with no clouds is ideal. It will however work quite well with very heavy cloud coverage, some trees, etc. Also, don't get this unit too wet and don't drop it on a rock hard surface, its not "ruggedized" or waterproof.
I assume you can charge it up at night. If you are going on long treks with no power for multiple days this would not be a good choice. A solar charger could be used but all combined that is a lot to carry.
I like the
Cube T7 (
http://www.cube-tablet.com/ for description but shop AliExpress and Internet shops for the best price. About 120 pounds or less if you shop around for it, with air express delivery (5-7 days total because getting stuff out of China always takes several days).
As far as ease of use you will like Android. Apart from the occasional reboot that you may need now and then everything works quite smoothly. There is a ton of free, high quality applications for Android and they are a snap to download and install (whenever you are in a WiFI area). This is an "all in one" unit and although its not cheap it packs an amazing amount of technology into something you can put in (a large) pocket.
Rick