Holt plc purchased a computer for £8,000 on January 1, 2018. Straight-line depreciation is used, based on a 5-year life and a £1,000 residual value. In 2020, the estimates are revised. Holt now feels the computer will be used until December 31, 2021, when it can be sold for £500. Compute the 2020 depreciation.