Abstract In this paper I examine the sensitivity of total UK Covid-19 deaths and the demand for intensive care and ward beds, to the timing and duration of suppression periods during a 500 day period. This is achieved via a SEIR model. Using an expected latent period of 4.5 days and infectious period of 3.8 days, R_0 was first estimated as 3.18 using observed death rates under unmitigated spread and then under the effects of the total lockdown (R_0=0.60) of 23 March.