BIM22020 - Meaning of trade: exceptions and alternatives: betting and gambling - spread betting
You should check the other guidance available on GOV.UK from HMRC as Brexit updates to those pages are being prioritised before manuals.
The principles of Down v Compston  21TC60 and Burdge v Pyne  45TC320 (see BIM22019) apply equally to spread betting. To be taxable, the spread betting wins must come not merely from an opportunity presented by a trade, they must arise from the carrying on of that trade. Whether or not a particular spread bet is taxable will depend on the terms of the contract and the economic substance of what is done.
For more on financial spread bets entered into by companies, see CFM50380.