Fuel gauge and speedo fault

[Acook85]

Hi, I have a fuel gauge problem with my 2004 2.0 HDI berlingo. My fuel gauge is saying empty with the fuel light on even tho I just filled the tank! Sometimes it will show the the right amount of fuel but 90% of the time it will show empty. Also sometimes if Iam doing high speeds (70mph) the speedo gauge will stop working as tho there is a loose wire, then go back to working fine. My rev counter and my thermo gauge has never had a problem. Please help!

I only know the basics about car repairs, but will it be a job I could possibly do myself? As I don't what to pay a garage a foutune unless I had no choice.
Any help would be grateful THANKS.

ANDY
UK