Let's do some guestimation...
The iceland study, when reported in the UK had tested 22,195 people, roughly 6% of the population of whom 1,364 had tested +ve and 50% of whom were asymptomatic and of those tested 4 had died.
Now 1,364 is the figure for people who currently have the virus as most people this would mean a multiplier of 341 from deaths...
BUT people only test positive for around 2 weeks.
Also assuming a case multiplier of 3 over a 2 week period and that the virus had only been in the country over an 8 week period the multiplier would be 505
(341 + 341/3 + 341/9 + 341/27)
So my guess is that around 4,028,890 people in the UK have had the virus. 7,978 (deaths) * 505 (multiplier). Or 6% of the population.
Double this figure if you only test positive for 7 days or if the very simplistic case multiplier is more than 3. I should work this out using a log function, but I'm two tired to be bothered.