I had this problem 4 years ago, which turned out to be the fuel pump - out of guarantee at 100k miles, it was a £2600 repair.
Two weeks ago, at 262k miles, the same problem started again. I have changed the fuel filter, and whilst it runs as good as when i first got it (at 11k miles) there is still some loss of power on occasions. I am hoping it isnt the pump again! Its been suggested that i should have the fuel tank drained and cleaned, along with the fuel lines, and at £150 it may be worth trying that next.