Afraid not - I was asking this question myself in another thread:
The rule on cyclists going at 20mph as part of Wales' new road laws
It seems that Wales' new 20mph law won't count for everyonewww.walesonline.co.uk
Cyclists are not legally required to have a speedo and therefore cannot be done for speeding, what they can be done for I think, is 'furious riding'.