Roseland
It is unknown whether the decision not to detour further away was due in part to a fuel constraint".
Well, unknown to you and I certainly, but I bet the answer comes out on the CVR, and is known to the BEA.
If started early enough a 20-40 nm detour adds an insignificant amount to the fuel burn.
Of course if you wait till you're face to face with the big painting on the radar, it's something else.