Revocation of retained EU law Transitional amendments Amendments to the Markets in Financial Instruments Regulation (MiFIR) and the European Market Infrastructure Regulation (EMIR) Systematic internalisers Execution of trades at the midpoint
‘Tick sizes’ set minimum increments (‘ticks’) by which prices for equities can change; in other words, they represent the smallest permitted price fluctuation for any particular equity. ‘Tick size regimes’ restrict so-called ‘midpoint’ trading. Midpoint trading is where a buyer and seller of a security are matched at a price that is half-way between (i.e. at the ‘midpoint’ of), for example, their respective offers to buy and sell. 16 In other words, tick size regimes prohibit or constrain trades happening where the price agreed is set at a fraction of the minimum increment (i.e. at a fraction of the tick size).
	The current UK tick size regime was introduced by the MiFID II Directive. It provides trading venues (regulated markets, MTFs and OTFs) with an exemption permitting midpoint trading that would otherwise involve a price movement below the tick size where the order is ‘Large In Scale’ (LIS). Whether an order is LIS is determined in accordance with Article 7 of Commission Delegated Regulation 2017/587.
	Article 63 of the Investment Firms Regulation 17 inserted Article 17a into MiFIR, which provided that systematic internalisers must comply with the tick size regime as well, although giving them the benefit of a similar exemption for midpoint trading on orders that are LIS. Bar this exemption, the prices at which systematic internalisers quote, offer improvements and ultimately enter into transactions must be in multiples of the stipulated tick size.
	The Act provides for systematic internalisers to be able to trade in equities with their clients at the midpoint in all circumstances, rather than only for orders that are LIS.