I had a Kindle Fire and returned it. The Kindle Fire is great for what it does (consumption of Amazon content), but it's quite locked down unless you're willing to root it. You can't sideload apps on the stock Kindle Fire (that was a breaking point for me) and the stock web browser (Silk) suffers from crashing tabs on a regular basis.
I bought a Kindle Fire HD awhile ago and I love it.
- I can sideload apps without rooting which means...
- you can install the browser of your choice and apps of your choice.
BUT... there are weaknesses to the Kindle.
- There is no youtube app by default- you're going to have to sideload the app. This is easy, but for a total newbie, this could be a dealbreaker
- Sideloading apps does not solve all of your problems- want gmail, gmaps, google voice, any google apps? You need root or transfer additional .apks that work behind the scenes- forget which one.
- I don't know about the UK, but I've heard that in other countries the selection of movies and all that blows compared to the US. So that's another thing to consider, since it really is a Amazon shopping tool.
The bottom line is that the Kindle Fire has a very specific purpose due to it's limitations for the average user. I still love my Kindle. But... I'd suggest a Nexus tablet. If they sell it in the UK.