"membership numbers of cycling organisations, in participation numbers in cycling events, in sales numbers"
But they only signify an increased interest in 'cycling'.
More members could mean more people wanting third party insurance or wanting to 'belong' or better marketing by those organisations.
Presumably it's analogous to people going to football matches for years and deciding to join the Supporters' Club - more members, no extra people spectating.
More people taking part in events, is partly because there are more events. It would certainly show up as more mileage if they were all measured - but I'm not convinced that it would be a significant amount. In general such events are not ridden by people who have 'just' started cycling.
An exception may be Pedal for Scotland. Presumably Cycling Scotland has done surveys to see if riding PfS has resulted in more people cycling more(?)
More bikes being sold means more N+1 and maybe more miles ridden. It also means some people buying bikes with the intention of using them, but deciding not to.
Dave has just written an entertaining piece on the QBC, it contains -
"cyclist numbers are just exploding, with virtual traffic jams on the canal and North Edinburgh Path Network as large numbers of ordinary looking people take to two wheels in an environment free of the tender mercies of the Edinburgh motorist."
http://mccraw.co.uk/qbc-swansong
Which is anecdotal, about Edinburgh (a very particular route) and recent.
If this is an increase (rather than just a blip caused by a few sunny days) and replicated more widely than one attractive/'safe' corridor then the figures should show up in next year's published surveys.
It's undoubtedly the case that there is more cycling going on - especially in parts of Edinburgh and London. It's also the case that short of all bikes having GPS, and automatically uploading data somewhere, the 'facts' will never be known.
However flawed the current system is, it shows an increase but not a massive one - and certainly not enough to give CEC or SG any confidence that its various 'targets' will be met.
Maybe time for some policy changes...