We present findings from the first two waves of an innovative, population-representative, UK time-use diary survey conducted both pre- and mid-lockdown, using an online diary instrument that proved both reliable and quick-to-field. Combining diary information on activity, location, and co-presence to estimate infection risks associated with daily behavior, we show clear changes in such behavior related to infection risk between the pre- and mid-lockdown periods: a substantial reduction of time spent in those behaviors with the highest levels of risk, accompanied by an equivalent increase in low-risk behavior. Because, in general, a populations' time use changes relatively slowly, the behavioral changes revealed may be interpreted directly as a consequence of the UK COVID-19 'lockdown' regulations. Subsequent waves will reveal the behavioral consequences of future changes in regulation.