Help! Runs great when cold, but terrible when hot!

Hello all,
New to the forum, and only recently a proud owner of a landrover! I have wanted one since I can remember, due to my dad having a series one since I was born - but I have only just been able to afford one (bought myself a 200tdi converted TD defender 90). Due to crazy insurance prices for young people...

Eitherway to the point - my landy was great for the first few months, had a few turbo issues with a pipe popping off, and one that was split... but my latest problem really has me stumped.

She seems to runs lovely when I first start her up from cold, but as soon as it has warmed up, it is sluggish as hell! We're talking changing down gears to get up mild hills... I have searched for similar symptoms on various forums without luck.
Also, I might note that I don't do very long distance drives, as I live on the Isle of Wight... but last night I drove maybe 10-14 miles (a reasonably long distance for the island haha) and as I was pulling into my drive, the engine completely died.

I just don't know where to start! Any help would be greatly appreciated! As shes my everydayer, and I really don't wanna be cycling to work!

Is she smoking at all when this happens and what colour?

She wasn't smoking at all...

My friend popped over a minute ago with a filter removing tool, so I was able to finally get my fuel filter off...
And what do I discover?? About half a beach.
All cleaned out, and new filter in - she runs like an absolute dream now! Far better than when I first bought it! I managed to reach the dizzying speed of 65mph on a short stretch of road near my house, and she still had more to give!
So I am very pleased and will be treating her to a trip to Slindon on Sunday, to get her nice and muddy!


Thanks for your help and speedy reply though! I was starting to get desperate, as I thought the symptoms where very odd, and I just didn't know where to start. Was blind luck that I stumbled across the problem!