Hard to say. Still pretty high numbers commuting in London Village even though the weather's cooling off.
Last year the numbers in my club mid-winter were around 100, same as we used to have mid-summer about 3 years ago. Be interesting to see if that's sustained this year.
Personally I think growth rates are unlikely to be sustained but growth will still continue - driving is such a rubbish experience - at least in the South East - and we do seem to have hit a tipping point of normalising it - which has always been CTCs argument for growth.
Anecdotally there's people at work and friends of mine who've been nowhere near a bike for years, who're starting to get into road riding. I think this is in part because they see how much the 'new' cyclists are enjoying it and enthusing about it. It's one thing for me to bang on about it but when they see 'someone like them' also loving it, they start to consider it for themselves.
Hopefully now the balance will tip and we'll start getting less hassle ...