Our conkers are getting smaller according to the Sunday Telegraph (16th September 2012). They feature the Conker Tree Science project, and report on an in-depth study (available here) looking at the diminishing size of conkers due to the horse-chestnut leaf miner.
The reports says that "last week, The Sunday Telegraph conducted its own survey of dozens of conkers,
found in Green Park and Hyde Park, in central London. Those which had fallen from heavily infested trees were, on average, 15 per
cent smaller than those from less affected trees – with an average diameter
of around 1 inch in diameter, while those from less effected trees were
around 1 1/4 inches."
Just like on the straw polls run during BBC Radio 4's Any Questions, it probably ought to be stated that their survey was not 'scientific' (for instance, they don't assess whether the trees not affected by the leaf miner also started off in better health?), but it's an interesting finding. I'm quite surprised, though, that they managed to find any trees in those areas which were not very heavily infested with the leaf miner!