These allowances apply for capital expenditure incurred between 1st April 2021 and 31st March 2023.  It should be noted that these allowances only apply to those paying Corporation tax i.e. not individuals or Partnerships.  In addition, the contract for plant and machinery (including fixtures and fittings) must have been entered into after 3 March 2021 and expenditure incurred (or obligated to be incurred within 4 months) after 1 April 2021, up to 31st March 2023.  

The super deduction gives relief at 130% of the qualifying cost, an uplift from the usual 18% writing down allowance for main pool plant and machinery assets. The Special rate allowance gives relief at 50% of the qualifying cost, a first year uplift from the normal 6% rate.

Unfortunately, these super deductions were not extended in the last budget and therefore, if an Investor wishes to take advantage of these allowances, the expenditure must be incurred before the 31st March 2023.  

The good news is that the Annual Investment Allowance (AIA) which gives 100% relief up to £1m, has been "permanently" set by the Chancellor, despite being previously due to reduce to £200,000 from April 2023.