I do sometimes wonder at some of the posts on fuel policy/usage, especially from so-called "professionals".
There are times in most pilots' careers when they, for whatever reason, get close to their destination with less fuel than they'd really like. Then the important issues are that they deal with this problem a) safely and b) in a commercially prudent manner. From what I read in this discussion, the crew of the NBO flight appear to have done perfectly well in both departments.
There are always those who say they would never end up in this situation because they always take "enough" fuel. Oh yeah? "Enough" for what and do you ever manage to get any payload on board after the wingtips have touched the tarmac?
For those who don't know, Nairobi is a classic hot'n'high airfield with some interesting terrain not far away, leading to possible weight restrictions on a long flight (not to mention any performance MEL items). Sometimes a decision might have to be made to offload passengers and/or freight to get more fuel on board; the crew may have actually taken greater than flight plan fuel in anticipation of delays into London but had it burn off due to being held down, etc.
Once en-route, the crew would have kept track of the fuel situation; they would know it would be tighter than normal at LHR but as long as they could arrive above Company minima, there would be a chance of getting in and if not, there would be plenty of nearby alternates. They would have considered a refuelling tech stop in somewhere like southern France but this would have had duty hours implications and been quite costly: much better to reach UK soil where an aircraft can be recovered quickly by a standby crew if neccessary. On receiving a 35-minute EAT from London, they made the decision to divert to Luton (could have been Stansted, Gatwick...) then during that diversion were offered a 'straight in' to LHR. In safety terms, they now had no delay into a 2-runway airfield as opposed to a single and in commercial terms they were saving a diversion; easy decision I'd have thought. The reasons for the PAN and subsequent MAYDAY have been explained well enough on this thread - I suspect speed control and vectoring around the TMA used a little more fuel than planned so the relevant agencies were kept informed in a timely manner.
The system works, what's the problem?