Many thanks for all of the replies, Hand Solo - the FCO ref was particularly useful.
In order to clarify matters, the first occassion I mentioned (3 mins...) we had used both our contingency and our diversion fuel whilst holding and had indeed reached our final 30 mins of fuel. We had 600kgs in one tank and 700kgs in the other on my after landing fuel calcuation, when our SWORD said 1200kgs was the absolute minimum. If we had had to go around I dread to think what would have happened - we made, as did everyone else that night, a SRA onto 23 at LHR, a siuation that was not entirely unexpected. Not the best approach to be trying to ignore the FMC that is desperately screaming 'using rsv fuel' at you. Please note on this occassion the capt did take SWORD fuel - no more though, and it was his dimissal of my levels of discomfort to not taking extra that I had a problem with.
On the flight this week, I was unsure as to how the ATC strike would affect us. SWORD allows for the longest routing from a departure runway to the longest arrival. However our company info informed us that several of the ATC areas we would be flying through would be on a minimum service, with no short cuts allowed. So with the potential for direct routings out of the window but everything else in the main OK, although I could not see a reason for extra fuel I certainly was not happy to take less.
In the end we requested a higher cruise level and slightly slower (more efficient) speed to arrive at destination with 30 mins + diversion. My comfort zone during the flight was not compromised, but the capts regard for my opinion left something to be desired.
I have learnt something from this situation. I could have written a CHIRP, but will not this time. I will be forewarned and forearmed next time I fly with this capt, and if producing the FCO and a general discussion about our previous flights doesn't work, I will be keeping the paperwork from the flight to discuss with someone a bit higher up than me.
Once again, thanks for your input.