its not legal now but i'm sure time trialists back then used 650 coz you spin faster right?
Not in the UK. You would have got some funny looks turning up to an event as a 'proper' TT'er with a 650 wheeled bike. Some people might even have hinted that you might have been a triathlete 'having a go at proper cycling'.
TBH, I can't see why you would spin faster with 650's? How does cadence relate to wheel size if the actual gear size is the same? ie - a 110" gear is the same with either 700c or 650c, you just use bigger chainrings or smaller sprockets with the 650's. I thought that triathletes started using 650's for aerodynamics as they present a smaller frontal area.
In the UK in CTT events you can basically ride what you like outside a few basic restrictions (eg - no discs on the front, rims no deeper than 80mm). These do not include dictating wheel size so you can still ride lo-pros with 24" front wheels or even a Moulton. It's only UCI controlled events that have the draconian restrictions on what you can ride.
Today is the yesterday of tomorrow.