Thanks for the info richardandhazel.
I think however that i have the problem cured!!!
I done the function test for the Thermoswitch as described on your link however there was no difference.
I also done the resistance test with a meter. Fig 7.7 is missing from the link but i got similar figures on my first test and as the car warmed up, the readings decreased.
As stated at the very start, both fuel pumps primed ok when i turned the key every time and this made me more or less rule out the relay but just to be on the safe side, i bought a new one.
Guess what? Problem gone!!!
The only thing i can figure is that somewhere inside the relay something has broke and as the relay heats up the problems occur. Maybe im wrong..who knows.