All right, decided to replace all main beam headlight and dipped beam bulbs, as a precaution.
Ordered OSRAM Night Breaker Unlimited H1 and GT Ultra 120 H7 - BUY ONE GET ONE FREE! from Powerbulbs (they have a 20% discount offer on at the moment). I hope the H1 are the correct fitting, I nearly went with H9, after reading dozens of threads on this forum, but H9 was not an option Powerbulbs gave, recommending H1 for my vehicle.
Halfords quoted me at over £8+ per bulb for fitting the dipped beam bulbs, not asked for a main beam quote, probably another £8 per bulb...at those prices, I will probably ask Chris at Tayport to help me out, as he did such a fine job for me on other repairs. After all, what's a 100 mile road trip to a diesel Tourer!