I reckon it'd be useful to have a full list of weights for Brompton parts so I figured I'd start with what I know and people can contribute to it over time. These are a mix of official weights and my own, don't know which are which unfortunately. Units are grams, obviously
Fork:
steel: 565
titanium: 350
Rear Frame:
steel: 755g
ti: 468g
Stem:
M: 806
S: 866
P: 602
Headset:
steel: 165
aluminium: 120
Handlebar:
M: 282
S: 132
P:
Brake Lever (single): 75
Seat Post:
standard, steel: 397
Pentaclip: 100
Saddle:
post-2009: 385
Crankset:
left arm: 190
44T right side: 288
44T chainguard: 57
Bottom Bracket (inc. crank bolts): 279
Chain:
SRAM PC1, 96 links: 280
Pedals:
Folding Pedal:
pedal: 240
bolt, steel: 41
washer: 8
Alloy, non-folding: 119
Front Hub:
standard: 158
superlight: 108
Tyres:
Brompton yellow Label: 240
Eazy wheel (not including fixings): 30