Your business year end, not 5 April, is relevant for capital allowances purposes. If however you are running a business and making up accounts to 31 March or 5 April, you should consider buying plant and machinery to take advantage of the Annual Investment Allowance (AIA). Note that the AIA was increased from £200,000 to £1 million on 1 January 2019, so the allowance for year ended 31 March 2019 would be £400,000, not the full £1 million (£200,000 x 9/12 plus £1 million x 3/12).
The AIA provides a 100% tax write off for equipment used in your business. This tax relief extends to fixtures and fittings within business premises such as electrical, water and heating systems. AIA does not apply to motor cars but there is a special 100% tax relief if you buy a new car that emits no more than 50g CO2 per kilometre.