Transport for London’s quarterly ‘Operational and Financial Performance Report’, which is published as part of the Finance and Policy Committee papers, includes a measure of the trend in the number of cyclists counted on London’s main roads (the Transport for London Road Network, or TLRN). The measure is an index set to 100 in the base period of March 2000, and according to the latest report the index reached a new high of 298 in the latest quarter (April to June 2011). This means that in this period there were about three times as many cyclists counted as using the TLRN as in March 2000.
The first chart below shows the quarterly trend in the index (and a four-quarter moving average), while the second chart shows the trend in the annualised change, i.e. the change from the same quarter a year ago. You can get the data for each chart in csv format here.